Copy metadata from wildcard GsApp objects to concrete GsApps

This allows us to set a wildcard that matches on some metadata (for instance, GnomeSoftware::FeatureTile-css) and this allows us to preserve the data without having to re-resolve the metadata in the concrete GsApp.

This allows us to ignore the problem where the system appstream plugin is no longer refining flatpaks, and thus higher priority GsApps were not getting the system-defined feature tile CSS metadata set.