Inbox: Add API to list conversations (#11110)

* Add API to list inbox conversations

* fix test + add api doc

* use `.lean()`

* orderBy after the the grouped conversations are loaded

* fix ordering

website/server/controllers/api-v3/inbox.js

@@ -12,6 +12,7 @@ let api = {};
  * @apiDescription Get inbox messages for a user
  *
  * @apiParam (Query) {Number} page Load the messages of the selected Page - 10 Messages per Page
+ * @apiParam (Query) {GUID} conversation Loads only the messages of a conversation
  *
  * @apiSuccess {Array} data An array of inbox messages
  */
@@ -22,9 +23,10 @@ api.getInboxMessages = {
   async handler (req, res) {
     const user = res.locals.user;
     const page = req.query.page;
+    const conversation = req.query.conversation;
 
     const userInbox = await inboxLib.getUserInbox(user, {
-      page,
+      page, conversation,
     });
 
     res.respond(200, userInbox);