Add links to view structural metadata artefacts
For these artefacts which are required in the generator:
- Category scheme
- Agency scheme
This could be done by having a separate link to the "main registry", and having fields with the agency scheme and category scheme. Consider:
- The goal of discovering the schemes without knowing the names. Query them all by: https://registry.sdmx.org/ws/public/sdmxapi/rest/agencyscheme/all/all/latest/?format=sdmx-2.1&detail=full&references=none
- Query a specific scheme by: https://registry.sdmx.org/ws/public/sdmxapi/rest/agencyscheme/all/AGENCIES/latest/?format=sdmx-2.1&detail=full&references=none