GeoSPARQL and OGC API Features Compability

[situx]

This pull request expands the gaps section on spatial data vocabulary with the following aspects:

• GeoSPARQL Compliance Benchmarking and SHACL shapes for graph validation
• Mappings from CQL to GeoSPARQL to use in OGC API Features implementations which act as frontends of triple stores
• Elaboration on the alignments between the GeoSPARQL vocabulary and 15 different vocabularies described in GeoSPARQL 1.1. Annex E Closes #1296 Closes #1358

Question for reviewers: Should this become a separate section, or is this still correctly referred to in this section?

[situx]

We have agreed to add two new best practices. One best practice for schema validation and one practice for compliance benchmarking, will emerge from the written text here. So this pull request will be reworked.

[situx]

I have removed the parts about validation and compliance benchmarking, which are likely to become separate sections and are worked on in other pull requests. Therefore, this pull request can be reviewed now.

[situx]

Merging this in as discussed in the last meeting