Prevent global censor rule creation

Censor rule creation results in expiry of all related content. On
WhatDoTheyKnow this would cause a major problem. This hacks in a
preventative measure. Admins who wish to create a global rule can seek
developer assistance until a more robust solution is found.

lib/controller_patches.rb

@@ -1,5 +1,15 @@
 # Please arrange overridden classes alphabetically.
 Rails.configuration.to_prepare do
+  AdminCensorRuleController.class_eval do
+    before_action :block_global_censor_rule_creation, only: [:create]
+
+    private
+
+    def block_global_censor_rule_creation
+      raise NotImplementedError if @censor_rule.is_global?
+    end
+  end
+
   HelpController.class_eval do
     prepend VolunteerContactForm::ControllerMethods
     prepend DataBreach::ControllerMethods