Document how to temporarily decommission/shutdown a tablet server

I have been asked a few times the "best" way to shutdown a tablet server or master server for common maintenance like an OS upgrade, disk swap, etc. Even if it's straightforward, perhaps adding a section to the documentation here we make users confident about their process.

I have heard of increasing the kudu-master_follower_unavailable_considered_failed_sec configuration to avoid re-replication during these short planned outages. Perhaps that tip could be added if appropriate.