[Feature Proposal][Rails Application Template] Add after_yarn hook

Right now, the rails new app_name --template /path/to/template.rb supports after_bundle scripts, but does not support after_yarn.

Because of that, I’m unable to create a template that’d support:

  1. Installation of NPM packages upon the project initialization.
  2. Coping yarn.lock file to my docker container via Dockerfile.
  3. Writing a .docker-compose.override.yml with the webpacker service and running docker-compose build command.

This happens because the bundle installs before the yarn does.

There’s a lot going on after the run bundle install, which is:

   run  bundle install
   run  bundle binstubs bundler
 rails  webpacker:install
create  config/webpacker.yml
create  config/webpack
create  config/webpack/development.js
create  config/webpack/environment.js
create  config/webpack/production.js
create  config/webpack/test.js
create  postcss.config.js
create  babel.config.js
create  .browserslistrc
 apply  /Users/me/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/webpacker-5.2.1/lib/install/binstubs.rb
 exist    bin
create    bin/webpack
create    bin/webpack-dev-server
append  .gitignore
   run  yarn add @rails/webpacker@5.2.1 from "."
   run  yarn add --dev webpack-dev-server from "."

How do you feel about adding the after_yarn?