Use RFC 4122 namespaced UUIDs

This configuration option disappeared in Rails 7.1 [1] (meaning it isn't
possible to set it to `false` in a Rails 7.1 application). Since it's
going to be our only option when upgrading to Rails 7.1, we're already
activating it now.

[1] https://github.com/rails/rails/commit/7b4affc78

config/initializers/new_framework_defaults_7_0.rb

@@ -80,7 +80,7 @@ Rails.application.config.action_controller.wrap_parameters_by_default = true
 #
 # See https://guides.rubyonrails.org/configuring.html#config-active-support-use-rfc4122-namespaced-uuids for
 # more information.
-# Rails.application.config.active_support.use_rfc4122_namespaced_uuids = true
+Rails.application.config.active_support.use_rfc4122_namespaced_uuids = true
 
 # Change the default headers to disable browsers' flawed legacy XSS protection.
 # Rails.application.config.action_dispatch.default_headers = {