### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

Using the serverless framework, when deploying a lambda function that uses a custom container runtime, the image is pushed to localstack with an "ImageUri" value that includes the docker image's digest (e.g. `localhost:4513/serverless-test-local@sha256:306d92[TRUNCATED]`). When executing that lambda function, fullstack uses the docker url that includes the digest, and improperly treats the portion after `:` as an image tag (https://github.com/localstack/localstack/blob/master/localstack/utils/docker_utils.py#L1203), causing the function to fail.

### Expected Behavior

Localstack should pull the docker image with the properly formatted digest and successfully execute the lambda function.

### How are you starting LocalStack?

With the `localstack` script

### Steps To Reproduce

#### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`)

    localstack start

#### Client commands (e.g., AWS SDK code snippet, or sequence of "awslocal" commands)
Sample serverless.yml
```
service: test
plugins:
  - serverless-localstack

frameworkVersion: '2'

provider:
  name: aws
  lambdaHashingVersion: 20201221
  ecr:
    images:
      test:
        path: ./test

custom:
  localstack:
    debug: true
    stages:
      - local
    host: http://localhost
    edgePort: 4566  
    autostart: true 
    docker:
      sudo: False

functions:
  test:
    image:
      name: test
```

Execute function
```
sls deploy --stage local
awslocal lambda invoke --function-name test-local-test /dev/null
```

Localstack error
```
2021-11-08T19:25:08:INFO:localstack.services.awslambda.lambda_executors: Running lambda: arn:aws:lambda:us-east-1:000000000000:function:test-local-test
2021-11-08T19:25:08:DEBUG:localstack_ext.services.awslambda.lambda_extended: Putting invocation event (request ID d01c1e28) for Lambda 'arn:aws:lambda:us-east-1:000000000000:function:test-local-test' to queue
2021-11-08T19:25:08:DEBUG:localstack_ext.services.awslambda.lambda_launcher: Executing custom image execution for image localhost:4513/serverless-test-local@sha256:306d925cd4f0188bcb9808c7715fc444dff3eee356415e58651db25304825221
2021-11-08T19:25:11:DEBUG:localstack.utils.docker_utils: Pulling image: localhost:4513/serverless-test-local@sha256:306d925cd4f0188bcb9808c7715fc444dff3eee356415e58651db25304825221
2021-11-08T19:25:11:DEBUG:localstack.utils.docker_utils: Repository: localhost:4513/serverless-test-local@sha256 Tag: 306d925cd4f0188bcb9808c7715fc444dff3eee356415e58651db25304825221
2021-11-08T19:25:12:ERROR:localstack_ext.services.awslambda.lambda_extended: Unable to invoke Lambda "arn:aws:lambda:us-east-1:000000000000:function:test-local-test": 
Traceback (most recent call last):
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/docker/api/client.py", line 268, in _raise_for_status
    response.raise_for_status()
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/requests/models.py", line 943, in raise_for_status
    raise HTTPError(http_error_msg, response=self)
requests.exceptions.HTTPError: 404 Client Error: Not Found for url: http+docker://localhost/v1.41/images/create?tag=306d925cd4f0188bcb9808c7715fc444dff3eee356415e58651db25304825221&fromImage=localhost%3A4513%2Fserverless-test-local

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/code/localstack/localstack/utils/docker_utils.py", line 1208, in pull_image
    self.client().images.pull(repository, tag)
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/docker/models/images.py", line 447, in pull
    repository, tag=tag, stream=True, all_tags=all_tags, **kwargs
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/docker/api/image.py", line 430, in pull
    self._raise_for_status(response)
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/docker/api/client.py", line 270, in _raise_for_status
    raise create_api_error_from_http_exception(e)
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/docker/errors.py", line 31, in create_api_error_from_http_exception
    raise cls(e, response=response, explanation=explanation)
docker.errors.NotFound: 404 Client Error for http+docker://localhost/v1.41/images/create?tag=306d925cd4f0188bcb9808c7715fc444dff3eee356415e58651db25304825221&fromImage=localhost%3A4513%2Fserverless-test-local: Not Found ("manifest for localhost:4513/serverless-test-local:306d925cd4f0188bcb9808c7715fc444dff3eee356415e58651db25304825221 not found: manifest unknown: manifest unknown")

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/localstack_ext/services/awslambda/lambda_extended.py", line 448, in do_run_lambda_executor
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/localstack_ext/services/awslambda/lambda_launcher.py", line 222, in docker_separate_execute_in_container
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/localstack_ext/services/awslambda/lambda_launcher.py", line 189, in custom_image_execute_in_container
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/localstack_ext/services/awslambda/lambda_launcher.py", line 148, in get_image_entrypoint_cmd
  File "/opt/code/localstack/localstack/utils/docker_utils.py", line 1212, in pull_image
    raise ContainerException()
localstack.utils.docker_utils.ContainerException
2021-11-08T19:25:12:INFO:localstack_ext.services.awslambda.lambda_extended: Lambda container output: None
None
2021-11-08T19:25:12:INFO:localstack.services.awslambda.lambda_api: Error executing Lambda function arn:aws:lambda:us-east-1:000000000000:function:test-local-test:  Traceback (most recent call last):
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/docker/api/client.py", line 268, in _raise_for_status
    response.raise_for_status()
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/requests/models.py", line 943, in raise_for_status
    raise HTTPError(http_error_msg, response=self)
requests.exceptions.HTTPError: 404 Client Error: Not Found for url: http+docker://localhost/v1.41/images/create?tag=306d925cd4f0188bcb9808c7715fc444dff3eee356415e58651db25304825221&fromImage=localhost%3A4513%2Fserverless-test-local

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/code/localstack/localstack/utils/docker_utils.py", line 1208, in pull_image
    self.client().images.pull(repository, tag)
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/docker/models/images.py", line 447, in pull
    repository, tag=tag, stream=True, all_tags=all_tags, **kwargs
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/docker/api/image.py", line 430, in pull
    self._raise_for_status(response)
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/docker/api/client.py", line 270, in _raise_for_status
    raise create_api_error_from_http_exception(e)
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/docker/errors.py", line 31, in create_api_error_from_http_exception
    raise cls(e, response=response, explanation=explanation)
docker.errors.NotFound: 404 Client Error for http+docker://localhost/v1.41/images/create?tag=306d925cd4f0188bcb9808c7715fc444dff3eee356415e58651db25304825221&fromImage=localhost%3A4513%2Fserverless-test-local: Not Found ("manifest for localhost:4513/serverless-test-local:306d925cd4f0188bcb9808c7715fc444dff3eee356415e58651db25304825221 not found: manifest unknown: manifest unknown")

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/code/localstack/localstack/services/awslambda/lambda_api.py", line 813, in run_lambda
    lock_discriminator=lock_discriminator,
  File "/opt/code/localstack/localstack/services/awslambda/lambda_executors.py", line 429, in execute
    return do_execute()
  File "/opt/code/localstack/localstack/services/awslambda/lambda_executors.py", line 419, in do_execute
    return _run(func_arn=func_arn)
  File "/opt/code/localstack/localstack/utils/cloudwatch/cloudwatch_util.py", line 158, in wrapped
    raise e
  File "/opt/code/localstack/localstack/utils/cloudwatch/cloudwatch_util.py", line 154, in wrapped
    result = func(*args, **kwargs)
  File "/opt/code/localstack/localstack/services/awslambda/lambda_executors.py", line 406, in _run
    raise e
  File "/opt/code/localstack/localstack/services/awslambda/lambda_executors.py", line 402, in _run
    result = self._execute(lambda_function, inv_context)
  File "/opt/code/localstack/localstack/services/awslambda/lambda_executors.py", line 710, in _execute
    result = self.run_lambda_executor(lambda_function=lambda_function, inv_context=inv_context)
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/localstack_ext/services/awslambda/lambda_extended.py", line 538, in run_lambda_executor
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/localstack_ext/services/awslambda/lambda_extended.py", line 436, in run_lambda_executor
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/localstack_ext/services/awslambda/lambda_extended.py", line 448, in do_run_lambda_executor
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/localstack_ext/services/awslambda/lambda_launcher.py", line 222, in docker_separate_execute_in_container
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/localstack_ext/services/awslambda/lambda_launcher.py", line 189, in custom_image_execute_in_container
  File "/opt/code/localstack/.venv/lib/python3.7/site-packages/localstack_ext/services/awslambda/lambda_launcher.py", line 148, in get_image_entrypoint_cmd
  File "/opt/code/localstack/localstack/utils/docker_utils.py", line 1212, in pull_image
    raise ContainerException()
localstack.utils.docker_utils.ContainerException
```


### Environment

```markdown
- OS: MacOS Big Sur 11.1
- LocalStack: 0.12.20
```


### Anything else?

_No response_
global SERVICE_PORTS, CONFIG_ENV_VARS
    SERVICE_PORTS = service_ports or parse_service_ports()
    globs = globals()
    protocol = get_protocol()
    
    for key, value in six.iteritems(DEFAULT_SERVICE_PORTS):
        key_upper = key.upper().replace("-", "_")
        
        port_var_name = "PORT_%s" % key_upper
        port_number = service_port(key)
        globs[port_var_name] = port_number
        url = "%s://%s:%s" % (protocol, LOCALSTACK_HOSTNAME, port_number)
        
        url_key = "TEST_%s_URL" % key_upper
        
        existing = os.environ.get(url_key)
        url = existing or url
        
        globs[url_key] = url
        
        os.environ[url_key] = url
    
    os.environ["LOCALSTACK_HOSTNAME"] = LOCALSTACK_HOSTNAME
    
    CONFIG_ENV_VARS += [
        "LOCALSTACK_" + v for v in CONFIG_ENV_VARS if not v.startswith("LOCALSTACK_")
    ]
    CONFIG_ENV_VARS = list(set(CONFIG_ENV_VARS))
def service_port(service_key):