Draft: systemd/systemd{-services}: enabled homed and add a service for nsss

Previously, systemd-homed was broken due to musl missing nss support. Thankfully, patching build-time to avoid relying on glibc was very easy and runtime is handled by skarnet's nsss daemon.

Partially depends on https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/76177 for the user/group to be satisfied for the systemd nsss service. Rejected because Alpine isn't switching to s6.(?) Will have to find some other way to generate the user/group. Maybe a postinstall in systemd-services?

Todo:

• Fix nsss config downstream since we can't do it upstream.
• Fix pam access issues (copy Arch Linux config?)