Upgrade react-webpack-rails-tutorial to Webpacker Lite

[justin808]

This change is 

[kevinhughes27]

I had to add HOT_RELOADING=TRUE to my Procfile in addition to these changes to ensure webpacker_lite is also expecting reloading.

https://github.com/shakacode/webpacker_lite/blob/master/lib/webpacker_lite/env.rb#L14
https://github.com/shakacode/webpacker_lite/blob/master/lib/webpacker_lite/configuration.rb#L24

[justin808]

@Judahmeek @kevinhughes27 is this something that should be added?

[kevinhughes27]

I was initially expecting REACT_ON_RAILS_ENV=HOT to set this up for me. I think ideally we wouldn't set 2 ENV vars in the Procfile but that's just my opinion.

[justin808]

@kevinhughes27, @Judahmeek, @conturbo, we need to finish up the half completed work of moving to React on Rails v8:

1. Remove REACT_ON_RAILS_ENV, as that's no longer used for v8. See search
2. Fix hot reloading in here: Possible to use React Hot Loader? #361

[kevinhughes27]

I'm happy to PR the REACT_ON_RAILS_ENV changes to the example repo. I started implementing the changes in #361 but given the state of my project I need to continue using the old hot reloader since I can't have a root component until I finish more refactoring. I'm not sure how many others would be in that state or how much the focus of react_on_rails is for old apps vs new apps.