Returns a list of metadata authorities that provided metadata on
the given target.
They can then be used to get the raw `extrinsic metadata <https://docs.softwareheritage.org/devel/glossary.html#term-extrinsic-metadata>`__ collected on
that object from each of the authorities.
This endpoint should only be used directly to retrieve metadata from
core SWHIDs (with type ``cnt``, ``dir``, ``rev``, ``rel``, and ``snp``).