### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

When attempting to sign some document using Localstack KMS inside a lambda container (also running on localstack), the localstack KMS listener returns some unknown error.

The KMS key and lambda containers have been created from the same CDK app deploy, and I can see all the resources in the localstack web console.

The test application I'm using to prove this behaviour is available here:
https://github.com/LukaHedt/localstack_kms_test

Instructions to run are in the main Readme, and the `/localstack/Readme.md` file.

`aws-sdk` returns an unknown error, and the localstack docker logs that I receive are available here:
https://pastebin.com/58Z3fXi3

Have done an amount of testing and can confidently claim the following:
- Have tested on multiple machines with the same outcome
- Doesn’t make a difference if I specify an ARN or a KeyID in the signing request
- Downgrading localstack versions either didn’t make a difference, or I couldn’t actually deploy a localstack container with version 0.12.20 or lower.

### Expected Behavior

KMS Sign should return a signature for the given payload.

### How are you starting LocalStack?

With a docker-compose file

### Steps To Reproduce

Test application demonstrating the current behaviour is available here:

https://github.com/LukaHedt/localstack_kms_test

Full instructions to run are in the `/localstack/Readme.md` file.


### Environment

```markdown
- OS: MacOS Monteray 12.3
- LocalStack: 0.14.0
```


### Anything else?

_No response_
"MAIN_CONTAINER_NAME",
    "OUTBOUND_HTTP_PROXY",
    "OUTBOUND_HTTPS_PROXY",
    "PERSISTENCE_SINGLE_FILE",
    "REQUESTS_CA_BUNDLE",
    "S3_SKIP_SIGNATURE_VALIDATION",
    "SERVICES",
    "SKIP_INFRA_DOWNLOADS",
    "SKIP_SSL_CERT_DOWNLOAD",
    "SQS_PORT_EXTERNAL",
    "STEPFUNCTIONS_LAMBDA_ENDPOINT",
    "SYNCHRONOUS_API_GATEWAY_EVENTS",
    "SYNCHRONOUS_DYNAMODB_EVENTS",
    "SYNCHRONOUS_KINESIS_EVENTS",
    "SYNCHRONOUS_SNS_EVENTS",
    "SYNCHRONOUS_SQS_EVENTS",
    "TEST_AWS_ACCOUNT_ID",
    "TEST_IAM_USER_ID",
    "TEST_IAM_USER_NAME",
    "TF_COMPAT_MODE",
    "THUNDRA_APIKEY",
    "THUNDRA_AGENT_JAVA_VERSION",
    "THUNDRA_AGENT_NODE_VERSION",
    "THUNDRA_AGENT_PYTHON_VERSION",
    "USE_SINGLE_REGION",
    "USE_SSL",
    "WAIT_FOR_DEBUGGER",
    "WINDOWS_DOCKER_MOUNT_PREFIX",
]
def is_local_test_mode() -> bool: