Uncomment non-validating data from the CCDH Pilot examples and fix CRDCH model so that they work correctly

[gaurav]

Currently non-validating data includes:

• In ccdh-pilot/demonstrator-1:
  • Field identifier can't be validated correctly.
  • Field quantity_measure can't be validated correctly.
  • Field execution_time_observation can't be validated correctly.
  • Field primary_site can't be validated correctly.
  • Field observations can't be validated correctly.
  • Field stage can't be validated correctly.
• In ccdh-pilot/demonstrator-2:
  • Field identifiers can't be validated correctly.
  • Field part_of can't be validated correctly.
  • Field associated_subject can't be validated correctly.
  • Field member_of_research_project can't be validated correctly.
  • Field primary_site can't be validated correctly.
  • Field observations can't be validated correctly.
  • Field diagnosis_date.date_time requires a complete date, not just a year. (see Add support for approximate dates ccdhmodel#130)

TODO: once PR #22 has been merged, this issue should be updated with links to the offending pieces of data.

[gaurav]

This appears to be caused by the bug identified in linkml/linkml#463.