fedora-bootc does not have a mechanism to add/remove package for a specific release

It's related to this MR !378

In fedora-bootc, since the repo definitions live in compose-images repo, the base-images repo is release-agnostic and don't define/require releasever. As a consequence, we don't have a mechanism to target a specific release in the manifests used in the modern path i.e not the legacy Pungi one.

In centos-bootc it's handle with branches i.e: one branch per release, but in fedora-bootc there is only the main branch.
One solution would be to move to the same branch structure.

Another solution is to bake releasever (or release or whatever) in bootc-base-imagectl to do so. The value would come from VERSION_ID included in /usr/lib/os-release from the source root. WDYT ?