Add function to request plain geojson output

[Sujanadh]

Description:

In FMTM we were working on OSM data conflation, where we request for plain geojson OSM features and conflate them with the field data. Currently there aren't any snapshot requests that provide plain geojson. Here, in this PR, I have added a function, request_plain_geojson_snapshot, which is used only based on the parameters, such as:

If,

bind_zip ----> True
output_type ---> Geojson
download_file ---> False

[spwoodcock]

Looks good!

Going to merge & we can look into the third option /custom/snapshot in another PR 👍