Handle UKI/Type1 boot entries properly

[Johan-Liebert1]

Currently in this function

bootc/crates/lib/src/bootc_composefs/boot.rs

Line 1250 in ca9f93c

pub(crate) async fn setup_composefs_boot(

we're relying on fs.transform_for_boot(&repo) to return boot entries in some particular order viz

1. Type1 entries in /boot/loader/entries (almost never used)
2. UKIs
3. Type1 Kernel + Initrd

We have been getting away with this even though our UKI images contain both UKI + (Kernel + Initrd) because the UKI appear earlier in the list. We should handle this more carefully