### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

We are using the `Authorization` header for routing purposes

```
 "authorization: AWS4-HMAC-SHA256 <...>"
```

https://github.com/localstack/localstack/issues/5770

### Expected Behavior

Use a custom header to avoid causing confusion with backend integrations

### How are you starting LocalStack?

With a `docker run` command

### Steps To Reproduce

Run a custom HTTP integration without authorisation

### Environment

```markdown
- OS: 
- LocalStack:
```


### Anything else?

No
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")
    if algorithm and credential and signature and signed_headers:
        return (
            f"{algorithm} Credential={credential}, "
            + f"SignedHeaders={signed_headers}, "
            + f"Signature={signature}"
        )
    return ""
def get_api_from_headers(headers, method=None, path=None, data=None):