Switch to using OSBuild for the live artifacts

[jlebon]

This is a follow-up to #1653. The main remaining work for fully moving over to OSBuild are the live ISO and PXE artifacts. The rationale for this is the same as in #1653.

[travier]

Should be ready now:

• osbuild: Add Live ISO/PXE build support coreos-assembler#3976
• live-iso: enable building with squashfs or erofs coreos-assembler#4012
• [next-devel] Enable 'erofs' by default for the rootfs in the Live ISO/PXE artifacts fedora-coreos-config#3365

[marmijo]

The fix for this went into next stream release 42.20250316.1.0. Please try out the new release and report issues.