Support Automatic Reboots

[lovesegfault]

Sometimes, such as when deploying a new kernel, it is desirable to reboot the system. It'd be nice if nixus supported this by having an auto-reboot functionality.

[infinisil]

Definitely something I'd like to implement. Here are some relevant links when I get to it:

• Request for fail-safe rollback feature NixOS/nixpkgs#65477
• Use fallback mechanism in GRUB to automatically recover unbootable system NixOS/nixpkgs#26332
• https://systemd.io/AUTOMATIC_BOOT_ASSESSMENT/
• https://www.gnu.org/software/grub/manual/legacy/Booting-fallback-systems.html

[lovesegfault]

I think when NixOS/nixpkgs#84204 is merged this will be relatively simple to do well. AIUI that is waiting on a systemd release, and then for that to make it's way into nixpkgs.

[lovesegfault]

As a stop-gap, just the ability to use boot instead of switch would also be useful. In particular I use nixus on my localhost to deploy to my localhost and would prefer to avoid runtime surprises (like sway auto-reloading my config and crashing as it usually does).