Adapt GetDataAvailability to schema and add GetObservation temporal filter conjunction for different valueReferences

- Adapt GetDataAvailability to schema
- Add resultTime to GetDataAvailability in gda:extension as swe:DataRecord
- Allow temporal filter in swes:extension of GetDataAvailability request to restrict matching resultTimes
- Add conjunction of temporal filters with different valueReferences in GetObservation
- Fix erroneous TimeInstant constructor for Date