Recover production replica(s)

Our production replica db2.cluster.gitlab.com is currently offline/not working, so we need to set it up again. Ideally we also set up another replica so we at least have 2, instead of 1 (until we roll out a better solution using e.g. pgpool and more replicas).

@jnijhof I'm assigning this to you as you said you were going to work on the replica anyway.