[DOC] Add documentation of geotile geopoint aggregation

[philvarner]

What do you want to do?

• Request a change to existing documentation
• Add new documentation
• Report a technical problem with the documentation
• Other

Tell us about your request. Provide a summary of the request and all versions that are affected.

From looking at the issues for supporting (e.g., opensearch-project/geospatial#92) geo aggregations for geoshapes, it seems that GeoTile aggregation is supported for geopoints. However, I was unable to find any documentation for this. There is documentation for geohash and geohex, but there doesn't seem to be any for geotile, so adding this would be useful.

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.

I was not able to find any other documentation on geotile aggregation support.