[Feature Request] Add clusters visualization style for Related Table-based (point) context layers

[janbur]

Overview

This can be implemented after: #141

Also linked to: #145

Clusters are a great way to visualize point data, especially when there are many overlapping points.

Solution

Add a clustered visualization style for point context layers based on 1) the count of clustered points, or 2) the aggregated value from an attribute. As GeoSight is using MapLibre, we could reuse: https://maplibre.org/maplibre-gl-js/docs/examples/cluster/

The clustered style should be defined at the Context Layer style config, either globally or overwritten at the project level, just like any other context layer style or label.