DGGRS definition schema and examples

[jerstlouis]

I have put together a proposal for a revised schema of DGGRS definitions:

https://github.com/opengeospatial/ogcapi-discrete-global-grid-systems/tree/master/core/schemas/dggrs-definition

It is now organized in three top-level objects:

• the DGGS (hierarchy),
• the ZIRS,
• the order of sub-zones.

It also allows to specify both a text identifier reference system as well as a 64-bit integer referencing system.
More properties are optional as some of the properties that were required might not always be relevant.

I also prepared one example for an ISEA3H DGGRS, following my presentation at the Delft meeting and the paper that we are working on with Marta, Perry and Luis.

I will also try to do more examples for the other DGGRSs that we implement.

Review and discussions welcome.
Once we are in agreement, it can replace the DGGRS schema at dggrs-definition.yaml (which I recently had to rename in order to distinguish the DGGRS definition that will sit on the DGGRS registry from the DGGS description returned at .../dggs/{dggrsId}. The DGGRS description always links to a DGGRS definition and if applicable, identifies itself as using a particular registered DGGRS using a URI. The DGGRS description provides additional information such as the default depth as implemented on the server.

@geofizzydrink @mpadillaruiz @ldesousa @allixender

[jerstlouis]

The proposed DGGRS definition schema is now included as informative Annex B:

https://docs.ogc.org/DRAFTS/21-038.html#_discrete_global_grid_reference_system_definition

including an example for an ISEA3H DGGRS.