Implement the Aggregation Extension

[jamesfisher-gis]

Is your feature request related to a problem? Please describe.

Both Elasticsearch and Opensearch have the functionality to aggregate geo_points and geo_shapes into geotiles, geohash, and h3. However the geo-aggregations in Elasticsearch are a commercial license feature. They are freely available in Opensearch.

The STAC API Aggregation Extension can be used to retrieve aggregations of STAC Items based on a search result from Opensearch or Elasticsearch.

Describe the solution you'd like Create an implementation of the STAC API Aggregation Extension. There is an open PR in stac-fastapi #684 that will add baseline support for the Aggregation extension.

Describe alternatives you've considered Opensearch does not yet support geo_shape aggregation to h3 hexagons. I wonder if an external STAC API plugin that utilizes STAC geoparquet and DuckDB for h3 aggregation could be useful...

Additional context The stac-server project has a node-based implementation of Aggregation..