Add moderation warnings (#9519)

* Add moderation warnings

Replace individual routes for disabling, silencing, and suspending
a user, as well as the report update route, with a unified account
action controller that allows you to select an action (none,
disable, silence, suspend) as well as whether it should generate an
e-mail notification with optional custom text. That notification,
with the optional custom text, is saved as a warning.

Additionally, there are warning presets you can configure to save
time when performing the above.

* Use Account#local_username_and_domain

app/controllers/admin/account_moderation_notes_controller.rb

@@ -14,6 +14,7 @@ module Admin
       else
         @account          = @account_moderation_note.target_account
         @moderation_notes = @account.targeted_moderation_notes.latest
+        @warnings         = @account.targeted_account_warnings.latest.custom
 
         render template: 'admin/accounts/show'
       end