### 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
if self.forward_url.hostname:
            forward_host = self.forward_url.scheme + "://" + self.forward_url.netloc
        else:
            forward_host = host
        forward_path_root = self.forward_url.path
        forward_path = path[len(self.base_url.path) :]  
        
        if forward_path and not forward_path_root.endswith("/"):
            if not forward_path.startswith("/"):
                forward_path = "/" + forward_path
        forward_url = forward_host + forward_path_root + forward_path
        return urlparse(forward_url)
class EndpointProxy(ProxyListener):