DEV: Allow all subdomains of localhost in development (#17018)

By default in rails, it looks like only one level deep is allowed.

config/environments/development.rb

@@ -110,4 +110,6 @@ Discourse::Application.configure do
       Bullet.rails_logger = true
     end
   end
+
+  config.hosts << /\A(([a-z-]+)\.)*localhost(\:\d+)?\Z/
 end