Switch Google Calendar Service to Gitlab CI for automated testing

I commited a .gitlab-ci.yml file for each branch (took the contents from the Drupal Association's template.gitlab-ci.yml ) and I can see that the pipelines are running ok:

I see some eslint and phpcs warnings but I'll address these in a different issue.

The file .gitlab-ci.yml can use some improvement, but the default template works for our project for now, I'll move this to "Fixed".

Automatically closed - issue fixed for 2 weeks with no activity.