CategoryCode available as valueReference in PropertyValue for DataRecord, BioBank use case

Hello everybody,

Following the samples hackathon held at the EBI on the 15th and 16th of March, various biobank representatives pointed out their need to use CategoryCode as valid type for the valueReference field in a PropertyValue of the DataRecord.
You can check the discussion we had during the meeting and the examples on how this has been implemented in the DataRecord examples by BBMRI-ERIC (Example <https://github.com/BioSchemas/specifications/blob/master/DataRecord/examples/bbmri-eric-ID-CZ_MMCI-collection-LTS_jsonld.json>, Discussion <https://docs.google.com/document/d/1xKFFLXcc6Db5wSuifOETpQSIFd73GLL2__2BNK9d4tk/edit#heading=h.aqwqtawny32k>).

Since the use of CategoryCode as valueReference looks more and more useful for various Bioschemas use cases  and not just for the Sample one, we would like to propose it as valid type for any property value used in Bioschemas and we would like to know what you think about this.

Look forward to getting your feedback
Kind regards,

Luca and Matt