service: Add some initial g_autoptr() support
service: Add some initial g_autoptr() support

This doesn’t bump our GLib dependency, since we already depend on GLib
2.44.

Signed-off-by: Philip Withnall <29c2a2ac2a854b9cf047275aa9de346d096be2e0@endlessm.com>

GNOME/dconf,GNOME/dconf,GNOME/dconf,GNOME/dconf