Enable 7.2 defaults and autloading of lib

Rails 3.0 changed how library loading works, and Zeitwerk rigidly enforces
this standard. So we now autoload the lib directory with the others.

config/application.rb

@@ -15,9 +15,15 @@ class Application < Rails::Application
     include GovukPublishingComponents::AppHelpers::AssetHelper
 
     # Initialize configuration defaults for originally generated Rails version.
-    config.load_defaults 7.0
+    config.load_defaults 7.2
     config.govuk_time_zone = "London"
 
+    # Prevents an initialisation error in Zeitwerk, initialisation changed as flagged by this comment
+    # in the Rails repo https://github.com/rails/rails/issues/37835#issuecomment-560563560
+    config.autoload_paths += [
+      Rails.root.join("lib"),
+    ]
+
     # Settings in config/environments/* take precedence over those specified here.
     # Application configuration should go into files in config/initializers
     # -- all .rb files in that directory are automatically loaded.