Review, test and recommend approach to Records theme classification

[rob-metalinkage]

The OGC API Records specification provides little guidance about how to define theme classifications - see opengeospatial/ogcapi-records#394

The proposal would be to review and test possible implementation patterns for description, API interactions and visualisation of metadata using these mechanisms and propose improvements.

These may include:

1. PR proposals to improve documentation of Records
2. Definition of specific profiles of Records with improved and predictable behaviours
3. Mapping transformations from Records to DCAT that includes resolution of theme keywords as unambiguous URIs
4. Documentation of implementation patterns and recommendations