Add DRS interface

[MariusDieckmann]

The internal data structure should allow easy exposition of datasets using GA4GH compatible interface: https://www.ga4gh.org/news/drs-api-enabling-cloud-based-data-access-and-retrieval/
This should be implemented, probably as a separate service?

[St4NNi]

Wrong repo. This should if any be stated in the server repo not in the documentation section.

[St4NNi]

Because this came back up recently, i guess we have all the building blocks already together, we just need to implement a small wrapper that implements DRS <-> Aruna at least for public repos