Update load balancing documentation to consider Praefect
We maintain an administration documentation for multi-node GitLab configurations regarding load balancing https://docs.gitlab.com/ee/administration/high_availability/load_balancer.html. For Praefect to enable a truly HA setup it needs to be configured to have a load balancer serving redundant Praefect nodes. For GitLab.com we do this using GCP Internal Load Balancers, but we should the aforementioned documentation to include generic pointers for all our users.
/cc @zj-gitlab