The base partition table handling for bootc should guess at the partitioning mode #2228
Description
Currently in pkg/distro/generic/bootc_imagetype.go in the genPartitionTableFsCust we set the default partitioning mode to raw. However, since users can provide base partition tables inside the container this isn't always true.
Let's instead of assuming raw guess based on the base partition table (scan the first level payloads to see if they contain lvm -> autolvm mode or btrfs -> btrfs mode, otherwise -> raw).
Leave the rest intact.
Some mystery is still how a btrfs base partition table works even if the container itself isn't set to default to btrfs (see the handling in the function). Not super relevant, but it irks me :)
Found while working on the documentation for disk.yaml: osbuild/image-builder-cli#462