Find Challenge - filter out "global" challenges

[mvexel]

I would like for us to be able to filter out "global" challenges (defined as challenges that cover more than 90 degrees longitude). This can be a checkbox.

[mvexel]

Exact definition of what "global" means to be iterated on.
If we choose 90 degrees that would exclude Russia.
Perhaps we can use bbox area instead. The earth is 16200 degrees squared (90*180)
How about we take half of that (8100) for bbox size. Is that cheap enough to calculate?

[mvexel]

As discussed let's try this with 8100 square degrees as a threshold for marking a challenge as "global". I'll create a follow up ticket to add a filter for this on the FE