Add feature flag for custom domains

Author: simonbaird

rails/lib/settings/features.rb

@@ -17,6 +17,12 @@ def subscriptions_enabled?(_user = nil)
     true
   end
 
+  def custom_domains_enabled?(user)
+    # While we're working on this feature I want to hide it
+    # from regular users.
+    user&.is_admin? || Rails.env.test?
+  end
+
   def redirect_tspot_to_url_enabled?(user)
     user&.is_admin? || user&.has_subscription?
   end