Implement sending messages to server add-on

Reviewed By: mweststrate

Differential Revision: D34073403

fbshipit-source-id: eacd73811b436f2b5c4255a83d8eb09367a96a67

desktop/flipper-common/src/server-types.tsx

@@ -580,6 +580,8 @@ export type ExecuteMessage = {
     params?: unknown;
   };
 };
+
+// TODO: Could we merge it with ClientResponseType?
 export type ResponseMessage =
   | {
       id: number;