Reenable systemd-resolved stub resolver

[agners]

Enable the systemd-resolved stub resolver and make it available on the hassio host network interface (172.30.32.1). This allows to use systemd-resolved directly from all containers.

Note that this makes /etc/resolv.conf point to the stub resolver running at 127.0.0.53 by default. This stub resolver isn't reachable from within containers. However, Docker does regnize this situation [1] and falls back to the alternate path at /run/systemd/resolve/resolv.conf, which is what /etc/resolv.conf is today. So this should not affect the initial /etc/resolv.conf in containers in practise.

This will however bind to port 53 and affect add-on potentially attempt to use that port. Add-ons should not bind to 127.0.0.53 or the hassio host network (172.30.32.1).

[1] https://github.com/moby/moby/blob/v28.0.4/libnetwork/internal/resolvconf/resolvconf_path.go#L51C32-L51C45