Verifies that the OM_Observation result type is valid according to the WaterML2 categorical timeseries observation . Tests
requirements from http://www.opengis.net/spec/waterml/2.0/req/xsd-categorical-timeseries-tvp-observation
Test requirement: /req/xsd-categorical-timeseries-tvp-observation/result result must contain an element in the substitution group headed by wml2:CategoricalTimeseries