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.