Update model annotations to use BIGINT for IDs (#5461)

All the migrations have been updated to use BIGINTs for ID fields in the DB, but ActiveRecord needs to be told to treat those values as BIGINT as well. This PR does that.

app/models/subscription.rb

@@ -11,8 +11,8 @@
 #  updated_at                  :datetime         not null
 #  last_successful_delivery_at :datetime
 #  domain                      :string
-#  account_id                  :integer          not null
-#  id                          :integer          not null, primary key
+#  account_id                  :bigint           not null
+#  id                          :bigint           not null, primary key
 #
 
 class Subscription < ApplicationRecord