Extend Geospatial support to include additional functions like st_envelope, st_buffer etc.

We have a geospatial usecase where we need to find the points in a polygon which Pinot can do really well with ST_Contains but what we need to do is fetch the Polygon by creating a Bounding box around a Point. Other tools for e.g postgis offers function like `ST_Envelope` to create this bounding box and `St_Buffer` to take a buffer for the radius.

Request is to add similar geometry capabilities to Pinot as well vs. having to manually define it.

cc @mayankshriv

Start by tracing Pinot's existing ST_Contains geospatial function and how geometry functions are exposed. Define the scope for ST_Envelope and ST_Buffer, including bounding-box and radius behavior, then verify the supported functions with focused geospatial tests.

Written by the indexing model from the issue text.