Crate bootupd

Bootloader updater.

This is an early prototype hidden/not-yet-standardized mechanism which just updates EFI for now (x86_64/aarch64 only).

But in the future will hopefully gain some independence from ostree and also support e.g. updating the MBR etc.

Refs:

• https://github.com/coreos/fedora-coreos-tracker/issues/510

Functions

backend_main
boot_update_main	Main entrypoint
frontend_main