Webpack setup refinements

[justin808]

We need to update

https://github.com/shakacode/react-webpack-rails-tutorial/tree/master/config/webpack

With the updates that have gone into:

https://github.com/shakacode/react_on_rails/tree/master/spec/dummy/config/webpack

and

https://github.com/shakacode/react_on_rails/blob/master/spec/dummy/config/webpacker.yml

Which are based on:

https://github.com/shakacode/react_on_rails_tutorial_with_ssr_and_hmr_fast_refresh

[jmtoporek]

If you still want help I'm willing to lend a hand

[ahangarha]

It seems files are updated. If there is any particular changes that are left, please list them.