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

app/models/follow.rb

@@ -10,6 +10,7 @@
 #  target_account_id :bigint(8)        not null
 #  show_reblogs      :boolean          default(TRUE), not null
 #  uri               :string
+#  notify            :boolean          default(FALSE), not null
 #
 
 class Follow < ApplicationRecord
@@ -34,7 +35,7 @@ class Follow < ApplicationRecord
   end
 
   def revoke_request!
-    FollowRequest.create!(account: account, target_account: target_account, show_reblogs: show_reblogs, uri: uri)
+    FollowRequest.create!(account: account, target_account: target_account, show_reblogs: show_reblogs, notify: notify, uri: uri)
     destroy!
   end