Move Praefect docs to the HA directory
Problem to solve
The HA docs for Gitaly are currently stored at https://docs.gitlab.com/ee/administration/gitaly/praefect.html. Before being generally available, we should move the docs to the same location as all the other HA documentation https://docs.gitlab.com/ee/administration/high_availability/gitaly.html
Proposal
Review the existing HA docs and update with content for HA Gitaly without NFS