add binaries shipped from git main

[cgwalters]

A cycle I've hit twice is basically adding a feature to bcvk to use in bootc and wanting to use it in CI (to also help verify the bcvk feature). It'd be handy to ship the binaries we have on git main via some mechanism that isn't GH releases. One thing I think could work well here is to use OCI artifacts stored on ghcr.io/bootc-dev/bcvk-binary or so.

Of course, we should do the same with packages when we eventually have those (but those we also want on the release).