Automated testing: Configure GitLab CI

Quick follow-up on this issue:

Added initial configuration of Gitlab CI pipelines with the most basic and minimum job requirements.
Left a few commented sections that could be enabled down the road to broaden tests coverage and enforce certain jobs.

Moving issue to Needs review since the tests are passing:
https://git.drupalcode.org/issue/login_switch-3497745/-/pipelines/428054

with warnings, that should most likely be addressed in different tickets (out of scope in this issue).

We would greatly appreciate if a maintainer with write access could take a look at merge request MR!5 and let us know if any more work would be required to get automated tests pipelines configured in the code base on Gitlab.

Feel free to let us know if you would have any questions or concerns on any aspects of this issue or the project in general, we would surely be glad to help.
Thanks in advance!

dydave → changed the visibility of the branch 3497745-fix-phpcs to hidden.

Super nice Matthew (@drupalmatts)!!

Thanks a lot for the speedy reply and for getting this in, it's super appreciated!

Any chance we could get a word from you on #3499850-5: Add module configuration schema file →
==> the dev branches are confusing ... for creating MRs and such...

+ possibly the co-maintainer offer 📌 Offering to co-maintain Login Switch Active
That's really up to you ... it's not like I don't have anything on my plate already 😅
But it would definitely allow to speed up the changes.

Cheers !