Add runner that can run QEMU

There are plans to run mutter and gnome-shell tests on top of VKMS virtual kernel mode setting. For this to be able to run in CI there needs to be a runner that is 1) privileged, and 2) has exported /dev/kvm.

These runners would only need to be able to handle pipelines on gnome-shell and mutter, and their forks.

There is currently nothing currently testable to run in such a CI, as there is no ready infrastructure in mutter to run such tests, so consider this a heads up that there will eventually be desired to have such CI capabilities.

This is how gitlab.freedesktop.org has configured runners for this: https://gitlab.freedesktop.org/freedesktop/helm-gitlab-config/-/blob/158db9a67a083ae206856844b9d830bc3c01ba89/gitlab-runner-provision/generate-cloud-init.py#L131