rust/sedona-spatial-join-geography: Support KNN join in geography join

After https://github.com/apache/sedona-db/pull/775 we have a join for geometry! This doesn't support geography; however, although some infrastructure exists to customize a distance metric in the internals. In geo-index we're hoping to remove the need for the `DistanceMetric` (https://github.com/georust/geo-index/issues/159) at which point it might be worth getting the interface right so that we can use S2's optimized distance predicates (perhaps even leveraging prepared distance, which other libraries can't do).

Start by reading pull request 775 and the geo-index issue 159, then inspect the existing geometry KNN join and the geography join's distance-metric infrastructure. The work is complete when geography supports KNN joins with an interface that can accommodate S2 optimized distance predicates.

Written by the indexing model from the issue text.