contaminant observation subclasses

[kschweikert]

us_sdwis:PWS-Observation is a pfas:PFAS-SampleContaminantObservation
me_egad:EGAD-PFAS-Observation has a different parent pfas:PFAS-ContaminantObservation, which should instead match the us_sdwis parent.

[kschweikert]

egad was updated so me_egad:EGAD-PFAS-Observation is a subclass of coso:ContaminantSampleObservation.

This reflects the latest coso, where the pfas: namespace has been eliminated as an intermediary.
SDWIS still needs to be aligned to latest coso