CI OCI autotagging should be smarter

[bleggett]

Currently if you try to oneshot build a single kernel version like: manual:exact=6.18.16;flavor=host

The CI scripts will update the published 6.18.16 OCI tag in the registry, but leave the 6 and 6.18 tags alone, referring to an older ref. This is confusing, unexpected, and not how semver tags work.

If you build and publish a full version off of main, it should update all the appropriate tagrefs for that version, always.

If we want to be able to build testing kernels, then we should support building and publishing off of non-main branches, and append the branch name to the tag(s).

This also overlaps a bit with #122 - we need the kmod directory, kconfig, and kernel image to have, at a minimum, an -edera suffix.