Add ktlint into CI

Description

Introduce style checks on CI.

I added a ktlint baseline file so that old code is OK.

We are now executing the gradle ktlintCheck task on each MR.

Let's experiment with that. I don't want to over-engineer this with git hooks for now.

Screenshots

Technical details

Tests

Issues

10 commandments of code review

👪 ❤️ https://gitlab.e.foundation/groups/e/-/wikis/contribute/development-processes/code-review-guidelines