Geo: Improve docs for re-attaching old primary to include multi-node archictures.
## Problem The [instructions for re-attaching an old primary as a secondary](https://docs.gitlab.com/ee/administration/geo/disaster_recovery/bring_primary_back.html) are tailored to single node (1K) architectures. It's difficult for customers with multi-node architectures to figure out what needs to be done to re-attach an old primary. ## Proposal Update the docs to include instructions for re-attaching an old multi-node primary as a secondary
issue