### 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_
import base64
import logging
import os
import re
import time
from collections import defaultdict
from functools import lru_cache
from io import BytesIO
from typing import Any, Dict, List, Optional, Union
from flask import Response
from localstack import config
from localstack.utils.aws import aws_stack
from localstack.utils.aws.aws_models import LambdaFunction
from localstack.utils.aws.aws_responses import flask_error_response_json
from localstack.utils.common import short_uid, to_str
from localstack.utils.container_networking import (
    get_endpoint_for_network,
    get_main_container_network,
)
from localstack.utils.docker_utils import DOCKER_CLIENT
LOG = logging.getLogger(__name__)
API_PATH_ROOT = "/2015-03-31"
LAMBDA_RUNTIME_PYTHON36 = "python3.6"
LAMBDA_RUNTIME_PYTHON37 = "python3.7"
LAMBDA_RUNTIME_PYTHON38 = "python3.8"