ENH: output format geoparquet

This came up in the STAC meeting today. Currently it looks like the supported output formats (available with the `f` query param) are: 'geojson', 'html', 'json', 'csv', 'geojsonseq', 'ndjson'. I got that list by naively trying https://firenrt.delta-backend.com/collections/public.eis_fire_lf_perimeter_nrt/items?f=geoparquet

It would be neat to add 'geoparquet' as an option.

Not sure if this is the right place to capture the request so feel free to close, just wanted to increase the visibility of that conversation.