Add option to be notified when a followed user posts (#13546)

* Add bell button

Fix #4890

* Remove duplicate type from post-deployment migration

* Fix legacy class type mappings

* Improve query performance with better index

* Fix validation

* Remove redundant index from notifications

spec/workers/refollow_worker_spec.rb

@@ -23,8 +23,8 @@ describe RefollowWorker do
       result = subject.perform(account.id)
 
       expect(result).to be_nil
-      expect(service).to have_received(:call).with(alice, account, reblogs: true)
-      expect(service).to have_received(:call).with(bob, account, reblogs: false)
+      expect(service).to have_received(:call).with(alice, account, reblogs: true, notify: false)
+      expect(service).to have_received(:call).with(bob, account, reblogs: false, notify: false)
     end
   end
 end