chore: bump React on Rails to v16.0.0 and Shakapacker to v8.4.0

- Update react_on_rails gem from 14.1.0.rc.0 to 16.0.0
- Update shakapacker gem from 8.0.0 to 8.4.0
- Update react-on-rails npm package from 14.0.3 to 16.0.0
- Update shakapacker npm package from 8.0.0 to 8.4.0
- Update Ruby version from 3.3.4 to 3.3.7
- Add migration plan document

Author: ihabadham

.ruby-version

@@ -1 +1 @@
-3.3.4
+3.3.7

Gemfile

@@ -6,7 +6,7 @@ git_source(:github) { |repo| "https://github.com/#{repo}.git" }
 ruby "3.3.4"
 
 gem "react_on_rails", "16.0.1.rc.4"
-gem "shakapacker", "8.2.0"
+gem "shakapacker", "8.4.0"
 
 # Bundle edge Rails instead: gem "rails", github: "rails/rails"
 gem "listen"