Set up GitLab CI [#3421073]

Problem/Motivation

Since Jun 2023, Drupal.org enabled GitLab CI for testing purposes. GitLab CI is now preferred over DrupalCI for testing.
This issue is to track progress towards getting a .gitlab-ci.yml file so that we can migrate away from the deprecated DrupalCI to GitLab CI.

GitLab CI documentation: https://www.drupal.org/docs/develop/git/using-gitlab-to-contribute-to-dr...

Benefits:

1) Testing is about five times faster
@see: https://www.drupal.org/about/core/blog/drupal-cores-gitlab-ci-testing-is...

2) Ability to configure tests in a more obvious and flexible way.

3) Great UI!

4) While we don't have tests in the module, we would still benefit from automated code style checks.

API changes

No API changes.

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