I noticed that openvpn3 is been clobbering my `/etc/resolv.conf` file. I
dug around a bit, and it turns out that upstream actually does have
support for systemd-resolved. I think it makes sense for us to
automatically enable that feature if the system is configured to use
systemd-resolved.
I opted to not change the default behavior of `pkgs.openvpn3`, but can
easily be convinced to change that if folks think I should.
conversions were done using https://github.com/pennae/nix-doc-munge
using (probably) rev f34e145 running
nix-doc-munge nixos/**/*.nix
nix-doc-munge --import nixos/**/*.nix
the tool ensures that only changes that could affect the generated
manual *but don't* are committed, other changes require manual review
and are discarded.