Hook into bootc's progress fd API

[jlebon]

So then e.g. the daemon could hook into this and update the BootcNode with progress every e.g... 30s or something? Mostly a quality-of-life/polish thing though this does becomes more relevant I think with #61.

See https://bootc.dev/bootc/experimental-progress-fd.html?highlight=progress#interactive-progress-with---progress-fd and bootc-dev/bootc#1016 for docs.