Initial GitLab + Postgres multi-container attempt

This seems to come up with GitLab on host port 3080

I copied the Gitea example from Awesome Compose, and then took a look at a Gist showing how to add PostgreSQL extensions

It turns out that manually adding the extensions is not necessary, this is done with Chef Omnibus when the GitLab container starts.

It is possible to change the database name from the default gitlabhq_production to a different name, such as gitlab as one customer did.