### 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
table.put_item(Item=event_data)
                response = requests_response(event_data)
                return response
        else:
            raise Exception(
                'API Gateway action uri "%s", integration type %s not yet implemented'
                % (uri, integration_type)
            )
    elif integration_type in ["HTTP_PROXY", "HTTP"]:
        if ":servicediscovery:" in uri:
            
            client = aws_stack.connect_to_service("servicediscovery")
            service_id = uri.split("/")[-1]
            instances = client.list_instances(ServiceId=service_id)["Instances"]
            instance = (instances or [None])[0]
            if instance and instance.get("Id"):
                uri = "http://%s/%s" % (instance["Id"], invocation_path.lstrip("/"))
        
        invocation_context.context = get_event_request_context(invocation_context)
        invocation_context.stage_variables = helpers.get_stage_variables(invocation_context)
        request_templates = RequestTemplates()
        payload = request_templates.render(invocation_context)
        if isinstance(payload, dict):
            payload = json.dumps(payload)
        uri = apply_request_parameters(
            uri, integration=integration, path_params=path_params, query_params=query_string_params
        )
        result = requests.request(method=method, url=uri, data=payload, headers=headers)
        
        invocation_context.response = result