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

lib/events/types.rb

@@ -25,6 +25,7 @@ module Events::Types
   TEAM_CHANGED = 'team.changed'
   CONVERSATION_TYPING_ON = 'conversation.typing_on'
   CONVERSATION_TYPING_OFF = 'conversation.typing_off'
+  CONVERSATION_MENTIONED = 'conversation.mentioned'
 
   # message events
   MESSAGE_CREATED = 'message.created'