[request] MR Challenge BBOX for GEOJson Input

It would be VERY cool to be able to specify a bounding box when creating a challenge that points to a geoJson file online.

We like to produce geojson files that have LOT's of rows in them and instead of having to generate different GEOJson files for each area, it would be so cool if there was an option in the challenge creation that would allow the challenge to be bounded by a bounding box or WKT that was specified. Then the generated challenge would only contain a subset of the rows from the GEOJson file. This would allow us to create multiple challenges from a single GEOJson file and each challenge would be a different area.

For instance, let's say I give you a link to a big GEOJson file:
https://daylight-map-distribution.s3.us-west-1.amazonaws.com/mr/atlas_checks/USA_LoneBuildingNodeCheck.json

And then I'd like to create a Challenge that points to that remote URL for input. BUT I want to specify a bounding box That includes just the area around Portsmouth New Hampshire. So I give it a WKT like this:

POLYGON((-70.83320006846051 43.102047963449316,-70.78513488291364 43.12836296408742,-70.73088988779645 43.068699385233934,-70.7058273267613 43.02956062541329,-70.74530944346051 42.99115027663405,-70.8211837720738 43.00897767392595,-70.85757598398786 43.04436604163545,-70.84178313730817 43.06518795251524,-70.85173949717145 43.09327378195965,-70.83320006846051 43.102047963449316))

or a bounding box like this:

POLYGON((-70.85757598398786 43.111071524153296,-70.69346770762067 43.111071524153296,-70.69346770762067 43.01073502451472,-70.85757598398786 43.01073502451472,-70.85757598398786 43.111071524153296))

And Map roulette would open the GEOJson URL and start reading each row but it would completely skip anything that was outside of the given bounding box.

I could imaging that this would be a checkbox right under the GEOJson URL that would enable the bounding box and give the user a field to paste the WKT into, or a field like the Location priority rule that gives the user the ability to paste in the bounding box or a map button to be able to draw it.

No files or tests are named. Start by tracing the challenge creation flow and the GEOJSON URL input, then determine where remote features are read and filtered. Done means a challenge can accept a WKT or bounding-box value and includes only features within that area, with the requested UI controls available.