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/settings.json

@@ -136,6 +136,7 @@
   "SIDEBAR": {
     "CONVERSATIONS": "Conversations",
     "ALL_CONVERSATIONS": "All Conversations",
+    "MENTIONED_CONVERSATIONS": "Mentions",
     "REPORTS": "Reports",
     "SETTINGS": "Settings",
     "CONTACTS": "Contacts",