### Is there an existing issue for this?

- [X] I have searched the existing issues

### Feature description

The use case I have in mind is to run Node 16.x Lambdas - the default container registry is `lambci/lambda` which is effectively abandoned. [Not even Node 14.x has been published](https://github.com/lambci/docker-lambda/pull/330). However, switching the registry over to [`amazon/aws-lambda-nodejs`](https://hub.docker.com/r/amazon/aws-lambda-nodejs) still fails to pull the container, since localstack is looking for the tag `nodejs16.x`. I'd like to be able to specify that if the runtime is `nodejs16.x` it just looks for tag `16`.

### 🧑‍💻 Implementation

_No response_

### Anything else?

_No response_
locks: Dict[str, Union[threading.Semaphore, threading.Lock]]
    creation_lock: threading.Lock
    def __init__(self):
        self.locks = {}
        self.creation_lock = threading.Lock()
    def assure_lock_present(
        self, key: str, lock: Union[threading.Semaphore, threading.Lock]
    ) -> Union[threading.Semaphore, threading.Lock]:
        with self.creation_lock:
            return self.locks.setdefault(key, lock)
LAMBDA_ASYNC_LOCKS = LambdaAsyncLocks()
class LambdaExecutor:
    """Base class for Lambda executors. Subclasses must overwrite the _execute method"""
    def __init__(self):
        
        self.function_invoke_times = {}
    def _prepare_environment(self, lambda_function: LambdaFunction):
        
        result = lambda_function.envvars.copy()
        
        aws_stack.inject_test_credentials_into_env(result)
        
        aws_stack.inject_region_into_env(result, lambda_function.region())
        return result
    def execute(
        self,