add support for logically bound images for anaconda ISO

[cgwalters]

We landed support for logically bound images to bootc; this transparently works when generating a qcow2 today with bib because we leverage bootc install to-filesystem. However, it doesn't transparently work with the Anaconda ISO because bib doesn't know how to inject these extra images into the lookaside cache on the ISO.

This also strongly relates to rhinstaller/anaconda#5197 where Anaconda itself would learn to use bootc install to-filesystem.

Connecting these threads, I think it would make sense actually to switch to using containers-storage: (unpacked representation, as opposed to dir for both the bootc image in the ISO and all LBIs).