PERF: Async notify users after inviting group (#12697)

Inviting a group generates a notification for each member. If this
happens synchronously it may take a while, leading to a poor user
experience.

spec/models/topic_spec.rb

@@ -982,6 +982,7 @@ describe Topic do
             set_state!(group, user_muted, :muted)
 
             Notification.delete_all
+            Jobs.run_immediately!
             topic.invite_group(topic.user, group)
 
             expect(Notification.count).to eq(3)

spec/models/topic_user_spec.rb

@@ -281,6 +281,7 @@ describe TopicUser do
           another_user = Fabricate(:user)
           group.add(another_user)
 
+          Jobs.run_immediately!
           topic.invite_group(target_user, group)
 
           expect(TopicUser.get(topic, another_user).notification_level)