Stagger "Patch All" so hosts aren't patched at once

"Patch All" (and multi-host patching) starts the run on every selected host at the same moment. On shared infrastructure, such as Proxmox nodes with many containers, that means every guest hits the package mirrors, CPU and disk together.

Request: an option to stagger multi-host patch runs, for example a maximum number of hosts patching at once or a delay between hosts, so large fleets can be patched without overloading the underlying hosts.

Originally raised on GitHub as #1080.