Add Rubocop

[C83]

Why ?

Rubocop will help us to keep our code clean, and consistant and will warn us about various optimizations/best practices along the way.

Must have:

• [x] Add Rubocop
• [x] Add Relaxed Rubocop (https://relaxed.ruby.style/)
• [x] Should look like base_robocop.yml Be sure to understand Everything in it
• [x] Run it and fix any issue already there (hint: rubocop -a try to autofix everything)

Reading list

• https://github.com/rubocop-hq/ruby-style-guide
• https://github.com/rubocop-hq/rails-style-guide

[C83]

1. gem 'rubocop', '~> 0.57.2', require: false to fix the version of rubocop and bundle install
2. gem "relaxed-rubocop" and inherit in .rubocop.yml file
3. In the file :
   • DisplayStyleGuide: true and DisplayCopNames: true show a link and the name of cop source
   • AllCops: Exclude to exclude few files of the verification
   • Style/FrozenStringLiteralComment: Enabled: false : blank line between comment and code is optionnal
   • Metrics/BlockLength: Exclude: The length of a line is 80. The rule is inactive with few directory
4. rubocop -a correct all "offenses". We can see the kind of cop and the rule's URL