[FEATURE] Add stats to GeoJSON exports

[emi420]

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

Data users needs to have a way to evaluate the datasets before download and use them.

Describe the solution you'd like

I would like have a file with dataset stats, like feature count and measurements for certain lines (ex: highways) and polygons (ex: land use)

Additional context

Users of HOT exports on HDX will benefit with this feature, specially if we develop a visualization to display into the site.