Add gitaly RunIt service to GitLab Omnibus
Closes: https://gitlab.com/gitlab-org/omnibus-gitlab/issues/1832
The package does not include the executable itself at this time.
We intend to initially ship it seperatly, to allow it to iterate in production on a seperate schedule from GitLab, at least initially.
But if you have the executable installed, and you enable the service, It should now be run using RunIt and available during gitlab-ctl status/up/down/restart