Apache Sedona spatial joins documentation page

[MrPowers]

This proposal is to write a documentation page explaining key spatial joins concepts, the different types of spatial joins, how to run spatial joins, and associated optimizations.

The docs have some great programming guides; see here:

We could create a concepts section in the programming guide because this content should be relevant across engines. Perhaps this URL:

• https://sedona.apache.org/latest/tutorial/concepts/spatial-joins/

Let me know if you think this would be useful!