message: Improve doc : Add thread owner API section
diff: @@ -649,6 +649,17 @@ controller.api.handover.request_thread_control('<RECIPIENT_PSID>', 'String to pa
  });
  ```
  +### Get Thread Owner
  +
  +Th Thread Owner API returns the app ID of the app the currently has thread control for a Page :
  +
  +- To get the app ID of the current thread owner :
  +```javascript
  +controller.api.handover.get_thread_owner('<RECIPIENT_PSID>', function (result) {
  +
  +});
  +```
  +
  ## Messaging type
  