Add gitlab version exporter to Ansible (GET)

@pguinoiseau noticed that the metric omnibus_build_info is not available in staging-ref. I'm not 100% sure of all the places where this metric is used, but he mentioned it's used by release tooling and in a release management dashboard so it would be good to get it added to GET.

Digging in a bit, it looks like we have a recipe in chef that pushes out a couple of cron jobs that output version info into files that node exporter then bubbles up. We should be able to do the same in Ansible.