Install cron `pi-hole up` during setup

Feature Request from Discord.

During installation offer the option to install cron or systemd timer to fire pi-hole up on schedule.

This would be nice for the un-monitored PiHole setups (like the one you install at you parents place) but what about people like me (ID10TS) that customize the install so much that there a risk of something going wrong during the install if you're not watching it.