Bring back puma.rb to target of app:update

This is a partial revert of rails#41083.

`puma.rb` may update by users, but  Rails has improved `puma.rb` sometimes.
For example, 06d614a and f719787.

To allow users to know those improvements, I think we should update
`puma.rb` by `app:update`.

Author: y-yagi

railties/lib/rails/generators/rails/app/app_generator.rb

@@ -128,7 +128,7 @@ def config
         template "application.rb"
         template "environment.rb"
         template "cable.yml" unless options[:update] || options[:skip_action_cable]
-        template "puma.rb"   unless options[:update]
+        template "puma.rb"
         template "storage.yml" unless options[:update] || skip_active_storage?
 
         directory "environments"