Force common formatting rules

[FSou1]

As a maintainer, I'd like to improve the source code readability. In order to do that, I think eslint and GitHub Superlinter are great options:

• [ ] GitHub Superlinter
• [x] ESLint

[FSou1]

• ESLint has been added;
• GitHub Superlinter is quite complicated to configure (local rules do not match with the remote ones, local linting does not work without docker), so it has been excluded;