feat: add bootc to Bluefin

[noelmiller]

Upstream Issue

https://github.com/ublue-os/main/issues/572

Purpose

We would like to test adding bootc to bluefin before adding it to main. Ideally, we should be able to test it here and then implement in main.

Things that need to change before merging

• [x] Putting booupctl command before initramfs step to see if it needs to be run before or after. This will help determine where this command needs to run (either in main or in the downstream)
• [x] Remove sl package
• [ ] Test enough to get a release of build-container-installer so we aren't using the main branch