CI: use podman/buildah now that the gitlab runners are not using docker

The gitlab freedesktop runners are not using docker, and so using docker-in-docker is not possible.

This project doesn't use ci-templates, but we can leverage some part of it to have the same results than currently by using podman and buildah on the ci-templates image we test on these runners.

Signed-off-by: Benjamin Tissoires benjamin.tissoires@redhat.com