dconf module: add dconf to services.dbus.packages

Some programs like eog seem to need dconf accessible on dbus.
Without this change I get

(eog:1738): dconf-WARNING **: 21:20:52.770: failed to commit changes to
dconf: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name
ca.desrt.dconf was not provided by any .service files