Endpoint: Value for the user submission search radius

[RyanTG]

In the app, we would like to offer options for the "Recent Activity" radius. Right now it is baked in at 30 miles.

We can discuss the preferred way to do that. One option might be to bake in 3 options: 30, 100, 150. Or something. Another option could be an endpoint where you can enter any value. But my concern there is that this would create an opportunity where someone could make giant requests.

https://github.com/scottwainstock/pbm/blob/2106c90f6d8be428830ea63efbd4eb6b506ed7bb/app/controllers/api/v1/user_submissions_controller.rb#L20

cc @bpoore

[RyanTG]

Duh, realized that you can set "max_distance" to whatever.