Add CI tools

Gitlab CI is now enabled on the merge request : https://git.drupalcode.org/project/ckeditor5_inline_quote/-/merge_reques...
After this will be merged on 1.0.x, coding standards will run on every branch and each commit.

The fact that CI pipelines are running on gitlab is enough to set that issue to RTBC.
New issues tickets should be created to fix errors and warnings reported by the CI tools when this will be merged.

@macsim thanks for your contribution!