Figure out how to reboot after "first-boot" init.d's

Note

• pi-os already has a "first-boot" init.d
• we can add multiple setup-once-{x}.initd

Feels like we want a generic /etc/init.d/first-boot dir/list.

• mechanism to add scripts that will be run only on the next boot (once).
• any/all of those scripts can signal that they need a reboot
• reboot should happen only after all startup init.d's are done

might be some tricks with systemd