feat: Activity messages for team assignments (#1893)

- assignment messages when the conversation team is changed
- change assignee based on team
- move round-robin and assignee logic to concerns

lib/events/types.rb

@@ -17,6 +17,7 @@ module Events::Types
   CONVERSATION_LOCK_TOGGLE = 'conversation.lock_toggle'
   CONVERSATION_CONTACT_CHANGED = 'conversation.contact_changed'
   ASSIGNEE_CHANGED = 'assignee.changed'
+  TEAM_CHANGED = 'team.changed'
   CONVERSATION_TYPING_ON = 'conversation.typing_on'
   CONVERSATION_TYPING_OFF = 'conversation.typing_off'