### Is there an existing issue for this?

- [X] I have searched the existing issues and read the documentation

### Question

A [recent commit](https://github.com/localstack/localstack/commit/f41b25cc8d68e97ce8eacd4374ded4a8072e50f6#diff-368e25a43c4a3200ecb9ae21e7b2a94da05d8eb24680bd6c2a37ee0e275bcd0aL67) scrapped the `{"features:initScripts":"initialized"}` feature that my team was relying on to bootstrap our development environment.

Basically we are putting a provisioning script in `/docker-entrypoint-initaws.d/` that installs Terraform and runs our Terraform definitions against `http://localhost:4566`. Then, the service that needs the AWS infrastructure has an entrypoint that polls `http://localstack:4566/health` and keeps looking for `{"features:initScripts":"initialized"}` in the response before attempting to actually start the service.

We found by trial and error that this was the most reliable way to bring up our stack, as opposed to looking for specific services to appear in the `/health` payload. However, now with this change we can't detect exactly when our Terraform provisioning finishes. It'd be great to get back that feature, or to have another way to detect when the LocalStack entrypoint has finished running the scripts in `/docker-entrypoint-initaws.d/`. For now we'll be sticking to `:0.12.19` instead of `:latest` as suggested.

Thank you.

### Anything else?

_No response_
target_url = target_url or "%s://%s:%s" % (get_service_protocol(), LOCALHOST, port)
    url = "%s%s" % (target_url, path)
    response = requests.request(method, url, data=data, headers=headers, verify=False, stream=True)
    return response
def get_auth_string(method, path, headers, data=None):
    """
    Get Auth header from Header (this is how aws client's like boto typically
    provide it) or from query string or url encoded parameters (sometimes
    happens with presigned requests. Always return in the Authorization Header
    form.
    Typically an auth string comes in as a header:
        Authorization: AWS4-HMAC-SHA256 \
        Credential=_not_needed_locally_/20210312/us-east-1/sqs/aws4_request, \
        SignedHeaders=content-type;host;x-amz-date, \
        Signature=9277c941f4ecafcc0f290728e50cd7a3fa0e41763fbd2373fcdd3faf2dbddc2e
    Here's what Authorization looks like as part of an presigned GET request:
       &X-Amz-Algorithm=AWS4-HMAC-SHA256\
       &X-Amz-Credential=test%2F20210313%2Fus-east-1%2Fsqs%2Faws4_request\
       &X-Amz-Date=20210313T011059Z&X-Amz-Expires=86400000&X-Amz-SignedHeaders=host\
       &X-Amz-Signature=2c652c7bc9a3b75579db3d987d1e6dd056f0ac776c1e1d4ec91e2ce84e5ad3ae
    """
    auth_header = headers.get("authorization", "")
    if auth_header:
        return auth_header
    data_components = parse_request_data(method, path, data)
    algorithm = data_components.get("X-Amz-Algorithm")
    credential = data_components.get("X-Amz-Credential")
    signature = data_components.get("X-Amz-Signature")
    signed_headers = data_components.get("X-Amz-SignedHeaders")