docs: decommission gitaly servers for migration
What
Change the migration plan to start with the newest Gitaly severs (nfs-file110) instead of the oldest one (file01)
Why
Before we where starting by draining nfs-file01
first and then moving to
nfs-file02
and onwards. However this becomes a problem when we want to
decommission the servers, we can't delete it because it's managed via
terraform. Deleting nfs-file01
by hand will result in terraform state
drift and it's not something we can easily solve.
Reference: https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/24124