### 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 not is_api_key_required:
        return True
    api_key = headers.get("X-API-Key")
    if not api_key:
        return False
    return validate_api_key(api_key, stage)
def update_content_length(response: Response):
    if response and response.content is not None:
        response.headers["Content-Length"] = str(len(response.content))
def apply_request_parameters(
    uri: str, integration: Dict[str, Any], path_params: Dict[str, str], query_params: Dict[str, str]
):
    request_parameters = integration.get("requestParameters")
    uri = uri or integration.get("uri") or integration.get("integrationUri") or ""
    if request_parameters:
        for key in path_params:
            
            request_param_key = f"integration.request.path.{key}"
            request_param_value = f"method.request.path.{key}"
            if request_parameters.get(request_param_key, None) == request_param_value:
                uri = uri.replace(f"{{{key}}}", path_params[key])
    if integration.get("type") != "HTTP_PROXY" and request_parameters:
        for key in query_params.copy():
            request_query_key = f"integration.request.querystring.{key}"
            request_param_val = f"method.request.querystring.{key}"
            if request_parameters.get(request_query_key, None) != request_param_val:
                query_params.pop(key)
    return add_query_params_to_url(uri, query_params)
def apply_response_parameters(invocation_context: ApiInvocationContext):