bootupd integration

[vkrizan]

Currently the bootc upgrade/switch commands do not install/add static grub configs (via bootupd). Note, that this feature was added to bootupd via coreos/bootupd#543.

This is essential part for supporting greenboot. Without installing grub static configs one has to have an image with already the grub configs installed or add them manually.

See also fedora-iot/greenboot#135.

Thank you.

[cgwalters]

We already install static grub configs, this is just about having bootupd support updating them. That's coreos/bootupd#639 over there.

(I know the fact that boot loader is not updated is confusing and we need to represent that here...at least probably in the status field)

[cgwalters]

#874 starts work on this (in theory of course we could handle external bootupd too, but it will help to have it inside this project).