### 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_
# Move existing alias to the new version
        new_version = lambda_client.publish_version(
            FunctionName=func_name, RevisionId=lambda_conf["RevisionId"]
        )
        snapshot.match("publish_version_2", new_version)
        new_alias = lambda_client.update_alias(
            FunctionName=func_name, FunctionVersion=new_version["Version"], Name=alias_name
        )
        snapshot.match("update_alias", new_alias)
        assert new_alias["RevisionId"] != new_version["RevisionId"]
        # lambda should now be provisioning new "hot" execution environments for this new alias->version pointer
        # the old one should be de-provisioned
        get_provisioned_config_result = lambda_client.get_provisioned_concurrency_config(
            FunctionName=func_name, Qualifier=alias_name
        )
        snapshot.match("get_provisioned_config_after_alias_move", get_provisioned_config_result)
        assert wait_until(
            concurrency_update_done(lambda_client, func_name, alias_name),
            strategy="linear",
            wait=30,
            max_retries=20,
            _max_wait=600,
        )  # this is SLOW (~6-8 min)
        # concurrency should still only work for the alias now
        # NOTE: the old version has been de-provisioned and will run 'on-demand' now!
        assert get_invoke_init_type(lambda_client, func_name, first_ver["Version"]) == "on-demand"
        assert (
            get_invoke_init_type(lambda_client, func_name, new_version["Version"])
            == "provisioned-concurrency"
        )