### 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
invocation_context.stage_variables = helpers.get_stage_variables(invocation_context)
                request_templates = RequestTemplates()
                payload = request_templates.render(invocation_context)
            except Exception as e:
                LOG.warning("Unable to convert API Gateway payload to str", e)
                raise
            
            headers = aws_stack.mock_aws_request_headers(
                service="kinesis", region_name=invocation_context.region_name
            )
            headers["X-Amz-Target"] = target
            result = common.make_http_request(
                url=config.service_url("kineses"), data=payload, headers=headers, method="POST"
            )
            
            invocation_context.response = result
            response_templates = ResponseTemplates()
            response_templates.render(invocation_context)
            return invocation_context.response
        elif "states:action/" in uri:
            action = uri.split("/")[-1]
            if APPLICATION_JSON in integration.get("requestTemplates", {}):
                request_templates = RequestTemplates()
                payload = request_templates.render(invocation_context)
                payload = json.loads(payload)
            else:
                
                payload = json.loads(data.decode("utf-8"))
            client = aws_stack.connect_to_service("stepfunctions")
            if isinstance(payload.get("input"), dict):