[NTR] Request for new kidney volume terms

### Completed template

https://docs.google.com/spreadsheets/d/1Pycj6k_pUCv0iaBe5CZEDS8cg4EcFnZwCQ-jBhl2GyU/edit?usp=sharing

### Any additional comments

There are 2 relevant, existing kidney size traits in OBA, and one existing kidney volume term, which is why I have requested new sub-type volume terms. 
Happy to discuss