Introduce CI

This is a very basic CI that will test whether the osinfo-db build succeeds in Fedora:rawhide and run "make check" afterwards.

There are many more jobs we could add to the CI pipeline.

The fedora:rawhide image is stored in the gitlab.gnome.org Gitlab instance, so we are reusing it. Alternatively, we could upload our own docker image to the gitlab.com registry. I don't see a compelling reason for the duplication for now.