Draft: main/postmarketos-base: don't depend on alpine-base

This is one possible solution to start cleaning up and preparing for the systemd branch. One of the problems there, is that alpine-base hard-depends on openrc. The solution in that branch was to fork and change the dependencies of the package. And we had the idea that maybe that would flow upstream. However, I had a look upstream, and that might be harder than expected because there is quite some complexity dealing with other things like devd several virtual providers around. I've still sent an MR, but not sure how will it be taken.

If that does not fly, the solution here is to take what's interesting for us from alpine-base into postmarketos-base, and disregard the rest. Then we can just have our pmb_select or equivalent packaging hack to select openrc or systemd. I'd rather have something nice integrated in alpine, but if that does not fly, I'd say this solution is better than forking alpine-base. The virtual for systemd is not implemented yet, so DON'T INSTALL this, as openrc will mostly likely be removed and the system will break down.

EDIT: Since upstream is too slow, I've split the busybox part of the MR into https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/65144 and then we can remove the dependency here