Add Bootc to Fedora 40 Based Images

[noelmiller]

Purpose

We want to add bootc to our images to start utilizing it. This is the direction things are going with the creation of new upstream images that rely on bootc.

We reverted PR #570 due to issues it caused with the installation ISO. This is because we did not include creating the metadata needed to allow the installation to complete.

Current Plan

We need to test bootc in downstreams before it can be added to main. There is currently a branch in Bluefin that is testing adding bootc and the required command to that container. I would also like to test in Bazzite next.

[m2Giles]

Learning from adding bootc to bluefin.

There are a few gotchas.

1. F39 and F40 behave differently. The metadata change must only occur on F40. F39 does not have the same requirement. If the metadata change happens on a F39 build, it will fail to install.
2. The metadata change must only ever be applied once. The change will persist across image builds. If it's applied more than once, it will error the build.
3. If Fedora makes the change to provide the metadata themselves, we will need to remove the metadata write we perform.

The change is being applied to bluefin today (22 June 2024). I think that instead of having this in main, this should be held at the downstream image level due to the potential footgun of making an image that cannot be installed.

[charles8191]

Adding this will also make Stable Atomic Variants like Debian, CentOS Stream, Almalinux, RockyLinux possible (at least for CentOS and AlmaLinux). Rocky Linux hasn't jumped onto bootc yet which is surprising as CIQ (their main sponsor) is all in on containers.