Add the gitlab-ci.yml file for the 1.0.x

As expected, the pipeline passed with some warnings: https://git.drupalcode.org/project/bambora/-/pipelines/528244

I'll open another issue to fix these PHPCS / PHPSTAN / CSPELL / ESLINT issues.

Move this to "Needs Review" for now.

I'll merge it to the main branch and mark it as "Fixed", I'll create another issue to fix the ESLINT / CSPELL / PHPCS / ...

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