oci: Allow reading metadata from labels too
oci: Allow reading metadata from labels too

Closes: #2978
Approved by: alexlarsson

matthiasclasen/flatpak,flatpak/flatpak,flatpak/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,flatpak/flatpak,matthiasclasen/flatpak,flatpak/flatpak,flatpak/flatpak,matthiasclasen/flatpak