Ethnicity

Like discussed in last night's GA4GH call, I'd like to propose opening up discussion on how to include ethnicity in phenopackets 2.0.

My impression from the discussion was that simple enumeration of values would not be enough. The problem is too complex. My opinion is that enumeration is great for simple, clear cut cases, but for complex issue the task of finding the solution should be moved outside phenopackets, i.e. to allow the use of ontology IDs.