`install to-disk` should not create a BIOS partition for composefs+UKI installations by default

[travier]

When installing an image using bootc install to-disk and selecting the composefs backend and using a UKI, bootc should not create a BIOS partition as it will not be used.

We may want to add an option to still add one if the system is expected or is immediately degraded into a kernel + initrd installation without a UKI.

Note that in Fedora CoreOS we may still choose to create those for compatibility but we will be using to-filesystem.

[Johan-Liebert1]

This one is trivial if we're installing the same image as the we're running in, but the complexity arises when we have a different target image, as we can't know off hand if the target image is going to be using UKI or not. I guess re-partitioning is an option