Add the main JH CI configuration file

This will need to change the project setting to point the default CI configuration file at jh/.gitlab-ci.yml.

The setting can be found at https://gitlab.com/gitlab-jh/gitlab/-/settings/ci_cd

I pushed a testing branch at https://gitlab.com/gitlab-jh/gitlab/-/commits/0-stable-jh and the pipeline is running there. I'll delete the branch after this is merged.

Closes #7 (closed)