Add metadata for rollback prevention

[sjg20]

UKI provides '.sbat' section with a list of version associated with the image.

When the image is loaded, this section can be inspected to see if any of the version are prohibited.

The SBAT documentation explains Shim uses this. UKI follows the same approach.

A sample UKI SBAT section is:

sbat,1,SBAT Version,sbat,1,https://github.com/rhboot/shim/blob/main/SBAT.md
systemd-stub,1,The systemd Developers,systemd,257,https://systemd.io/
systemd-stub.fedora,1,Fedora 

For FIT, we should be able to create something a little nicer, using metadata rather than a CSV file.