Create systemd-{network,resolve} user/group unconditionally

This shuts up this error from dbus:

May 11 13:52:16 machine dbus-daemon[259]: Unknown username "systemd-network" in message bus configuration file
May 11 13:52:16 machine dbus-daemon[259]: Unknown username "systemd-resolve" in message bus configuration file

which happens because the D-Bus config for networkd/resolved is
enabled unconditionally, and we don't have an easy way to turn it off.

(cherry picked from commit f19b58fb6a5cc55af6d8d8ca7979f8e64255d2d0)

nixos/modules/system/boot/networkd.nix

···
     environment.etc."systemd/network".source =
       generateUnits "network" cfg.units [] [];
 
-    users.extraUsers.systemd-network.uid = config.ids.uids.systemd-network;
-    users.extraGroups.systemd-network.gid = config.ids.gids.systemd-network;
-
     systemd.services.systemd-networkd = {
       wantedBy = [ "multi-user.target" ];
       before = [ "network-interfaces.target" ];

nixos/modules/system/boot/resolved.nix

···
       DNS=${concatStringsSep " " config.networking.nameservers}
     '';
 
-    users.extraUsers.systemd-resolve.uid = config.ids.uids.systemd-resolve;
-    users.extraGroups.systemd-resolve.gid = config.ids.gids.systemd-resolve;
-
   };
 
 }

nixos/modules/system/boot/systemd.nix

···
         ${pkgs.acl}/bin/setfacl -nm g:wheel:rx,d:g:wheel:rx,g:adm:rx,d:g:adm:rx /var/log/journal || true
       '';
 
+    users.extraUsers.systemd-network.uid = config.ids.uids.systemd-network;
+    users.extraGroups.systemd-network.gid = config.ids.gids.systemd-network;
+    users.extraUsers.systemd-resolve.uid = config.ids.uids.systemd-resolve;
+    users.extraGroups.systemd-resolve.gid = config.ids.gids.systemd-resolve;
+
     # Target for ‘charon send-keys’ to hook into.
     users.extraGroups.keys.gid = config.ids.gids.keys;