feat: Add a view for mentions (#3505)

- Added a new table mentions for saving user mentions
- Added a filter conversation_type in the API
- Added a view to see the mentions

app/javascript/dashboard/i18n/locale/en/chatlist.json

@@ -7,6 +7,7 @@
       "404": "There are no active conversations in this group."
     },
     "TAB_HEADING": "Conversations",
+    "MENTION_HEADING": "Mentions",
     "SEARCH": {
       "INPUT": "Search for People, Chats, Saved Replies .."
     },