### 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
parsed_url = urlparse(request.url)
        path_with_params = path_from_url(request.url)
        method = request.method
        headers = request.headers
        headers[HEADER_LOCALSTACK_REQUEST_URL] = str(request.url)
        response = modify_and_forward(
            method=method,
            path=path_with_params,
            data_bytes=data,
            headers=headers,
            forward_base_url=forward_url,
            listeners=listeners,
            client_address=request.remote_addr,