text: Title: [Umbrella] Revisit Ray dashboard API status code
  Body: ### Description
  
  Before https://github.com/ray-project/ray/pull/51417, the Ray dashboard APIs only returned 200 for success and 500 for errors; they didn't support status codes such as 404. Take #51417 as an example, it returns 404 when users try to kill a non-existent actor.
  
  ### Use case
  
  _No response_