[Feature] : Geo Hex Grid Aggregation on Geo Shape field

[heemin32]

Is your feature request related to a problem?
Similar to GeoHashGrid aggregation, GeoTileGrid aggregation, GeoBounds aggregation, we want to have GeoHexGrid aggregation on GeoShape.

What solution would you like?
Currently, we only support GeoHexGrid aggregation on GeoPoint. We want to support it on GeoShape as well.

What alternatives have you considered?
Not supporting it.

Do you have any additional context?
#194
#191
#97