annotate models (#2697)

* add annotate to Gemfile

* rails g annotate:install

* configure annotate_models

* add schema info to models

* fix rubocop to add frozen_string_literal

app/models/subscription.rb

@@ -1,4 +1,18 @@
 # frozen_string_literal: true
+# == Schema Information
+#
+# Table name: subscriptions
+#
+#  id                          :integer          not null, primary key
+#  callback_url                :string           default(""), not null
+#  secret                      :string
+#  expires_at                  :datetime
+#  confirmed                   :boolean          default(FALSE), not null
+#  account_id                  :integer          not null
+#  created_at                  :datetime         not null
+#  updated_at                  :datetime         not null
+#  last_successful_delivery_at :datetime
+#
 
 class Subscription < ApplicationRecord
   MIN_EXPIRATION = 3600 * 24 * 7