[feature] Add a Data Package serializer

[roll]

Purpose

Data Package is a European Commission-funded project (via NLnet) that is a standard containing a set of lightweight specifications for describing datasets and individual data files. The standard is widely used for data interoperability in other data portal systems like CKAN, Dryad, Our World in Data, and others. The main benefit of adoption the Data Package Standard is a rich set of software for reading and validating datasets - https://datapackage.org/standard/software/ (the most advanced implementations are in Python and R, as well as a Desktop application).

By creating this pull request, we would like to bootstrap a discussion if OSF would consider accepting the datapackage.json format to be one of the export targets for datasets' metadata. Also, tagging our friends from the University of California @sdiggs and @sapetti9 from Open Knowledge Foundation.

Thanks a lot in advance!

Changes / QA Notes

It only adds a new serializer without touching the existent code. Also, it exposes the new serializer in the osf.metadata.serializers.METADATA_SERIALIZER_REGISTRY

Documentation

Can you please help with identifying whether some docs need to be updated?

Side Effects

No

Ticket

No