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Having upgraded to the latest LocalStack version, I've noticed that Docker containers from Lambda executions are immediately removed when they terminate.

This was added in https://github.com/localstack/localstack/pull/1584

I can appreciate the need to clean up containers, however this feature of having them stay up is actually very useful for debugging things when they go wrong!

Would it be possible to have a flag so that when running LocalStack we can specify whether to remove containers on completion? Something like:

```
services:
  localstack:
    image: localstack/localstack:latest
    ports:
      - "4567-4593:4567-4593"
    environment:
      - SERVICES=serverless,ssm,stepfunctions
      - DOCKER_HOST=unix:///var/run/docker.sock
      - LAMBDA_EXECUTOR=docker
      - REMOVE_CONTAINERS_ON_LAMBDA_TERMINATE=true #(or false)
    volumes:
      - "${TMPDIR:-/tmp/localstack}:/tmp/localstack"
      - "/var/run/docker.sock:/var/run/docker.sock"
```

Thanks for the great work folks!
bucket_name = normalize_bucket_name(bucket_name)
    response = Response()
    exists, code = bucket_exists(bucket_name)
    if not exists:
        response.status_code = code
        return response
    if not isinstance(cors, dict):
        cors = xmltodict.parse(cors)
    BUCKET_CORS[bucket_name] = cors
    response.status_code = 200
    return response
def delete_cors(bucket_name):
    bucket_name = normalize_bucket_name(bucket_name)
    response = Response()
    exists, code = bucket_exists(bucket_name)
    if not exists:
        response.status_code = code
        return response
    BUCKET_CORS.pop(bucket_name, {})
    response.status_code = 200
    return response
def append_cors_headers(bucket_name, request_method, request_headers, response):