feat: add prettier as formatter

[Galimede]

What does this PR do?

• This PR introduces Prettier as a formatter for our codebase
• It also includes the update of Stylelint since Prettier will format the CSS and that Stylelint doesn't format anymore
• Note: ESLint was not updated here as the release was too recent and not every plugins are up to date yet
• Note: this PR also changed the Node version we use to the latest

How to review

• Check the commits
• npm install and use the new command : npm run format and see the changes by yourself locally
• Check that everything is working fine with the new Node version
• Don't hesitate to play with the Prettier config and especially with the printWidth rule
  • I've set it to 120 because we have pretty long lines and it was easier to read HTML in our components
  • But feel free to play around with it while it's not fixed yet

TODO

• [ ] Update files with the new order from Stylelint (can be done in a separate PR)
• [ ] Apply the formatter to the files (can be done in a separate PR)
• [x] Add the format:ci to our GitHub action

[florian-sanders-cc]

:wave: Hey there thanks for testing & setting up all of this @Galimede

My only question is: could we open a new issue about sorting imports with prettier? What do you think about trivago/prettier-plugin-sort-imports?

Reading through Hubert's feedback, I have one question:

Who runs the format:ci?

Should we add this in a GitHub action?
Maybe it should be in prepack?
Maybe in a precommit hook?

I'm not sure but I wonder if CI should format. Formatting means files would be modified and these modifications would need to be commited no? While it is possible to commit & push stuff from an action, I would rather use prettier --check ... to let the CI fail if formatting is missing so people can format and push formatting as part of their commits (not a commit dedicated to formatting I mean) before a PR is merged :thinking:

TLDR; no format:ci & a format:check-ci instead?