gitlab_runner: Add VM based executor (libvirt-executor)

For some workloads running in a container is too restrictive, ex:
arch-boxes (loop device, filesystem mount, pacstrap) and archiso
(pacstrap). Currently they both run a TCG accelerated QEMU VM, which is
very slow and painful to work with. We should provide a better option to
our users!

This adds a hardware accelerated VM for this kinds of workloads, which
is way faster and you can do whatever you like (mostly)!

Fix #283

---

TODO:

• Enable KSM?
• Get archiso to build
  • Done: https://gitlab.archlinux.org/klausenbusk/archiso/-/pipelines/10976
• Use BUILD_FAILURE_EXIT_CODE and SYSTEM_FAILURE_EXIT_CODE: https://docs.gitlab.com/runner/executors/custom.html#error-handling
• Fix existing users to use the secure-vm tag

roles/gitlab_runner/files/libvirt-executor

@@ -123,7 +123,7 @@ run() {
   vm_name="$(get_vm_name)"
   wait_for_ssh "${vm_name}"
   # Upstream issue: https://gitlab.com/gitlab-org/gitlab-runner/-/issues/28189
-  if [[ "${2}" == 'upload_artifacts_'* ]]; then
+  if [[ "${2}" == *'_artifacts'* ]]; then
     ssh 'TMPDIR=/var/tmp bash' < "${1}" || exit "${BUILD_FAILURE_EXIT_CODE:-1}"
   else
     ssh bash < "${1}" || exit "${BUILD_FAILURE_EXIT_CODE:-1}"