Add LAVA to docker-compose.yml

This renames docker-compose.yml to be docker-compose-gitlab.yml, and adds a new docker-compose containing LAVA instead of Gitlab as the OIDC client.

It does not add selenium testing for LAVA, but it does rely on the merge of the LAVA MRs to work (obviously).

This is part of https://phabricator.apertis.org/T7958.