Add field: samplingFrequency

[timvdstap]

Determine whether CIOOS Profile V3 has a field for sampling frequency, perhaps in MD_DataIdentification? If not, we should identify relevant ISO field, and bring it up with the Metadata TT. In the context of biological data sampling/processing, sampling frequency can help populate the required IPT-field studyExtent.

[timvdstap]

Some light reading: https://mcp-profile-docs.readthedocs.io/en/stable/extensions/samplingFrequency/index.html#samplingfrequency

MD_MaintenanceInformation seems to only touch on the frequency with which changes and additions are made to the resource after the initial resource is completed.