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

app/models/concerns/round_robin_handler.rb

@@ -0,0 +1,26 @@
+module RoundRobinHandler
+  extend ActiveSupport::Concern
+  include Events::Types
+
+  included do
+    after_save :run_round_robin
+  end
+
+  private
+
+  def run_round_robin
+    # Round robin kicks in on conversation create & update
+    # run it only when conversation status changes to open
+    return unless conversation_status_changed_to_open?
+    return unless should_round_robin?
+
+    ::RoundRobin::AssignmentService.new(conversation: self).perform
+  end
+
+  def should_round_robin?
+    return false unless inbox.enable_auto_assignment?
+
+    # run only if assignee is blank or doesn't have access to inbox
+    assignee.blank? || inbox.members.exclude?(assignee)
+  end
+end