Set up a Gitlab instance

We are going to evaluate Gitlab as a replacement for trac, gitweb.tpo, git-rw.tpo, github.com.

This ticket tracks the progress of the setup of a Gitlab service.

cf https://trac.torproject.org/projects/tor/wiki/org/meetings/2019BrusselsAdminTeamMinutes#gitlabservice

1. #33922 (closed) hardware requirements and planning
2. #29402 (closed) VM creation
3. #29401 (closed) LDAP group
4. #32730 (closed) migration from dip
5. #30857 (closed) migration from trac, phase I: tickets

Postponed post-launch:

• gitlab#49 (closed) monitoring
• gitlab#36 (moved) Phase II: git migration policies.
• other issues with gitlab are in https://gitlab.torproject.org/tpo/tpa/gitlab/-/issues