Enhance random rows feature to support UUID primary keys

I'm spinning this off from https://github.com/GoogleCloudPlatform/professional-services-data-validator/issues/1345 in order to manage the scope of the work. We do need this support but first we should get the basics in place.

Enable test `test_row_validation_uuid_rr_oracle_to_postgres` in `test_oracle.py` to produce the problem.