Add localhost to allowed hosts

In order for the forms-runnner review apps to make API calls to the
forms-admin app in the review app environment we need to allow
localhost as an allowed host.

Author: stephencdaly

lib/host_patterns.rb

@@ -5,5 +5,6 @@ module HostPatterns
     /admin\.internal.[^.]*\.forms\.service\.gov\.uk/,
     /pr-[^.]*\.admin\.review\.forms\.service\.gov\.uk/,
     /pr-[^.]*-admin\.submit\.review\.forms\.service\.gov\.uk/,
+    "localhost",
   ].freeze
 end