Document spatial Left Join

[alexeyegorov]

Based on this discussion about spatial joins, I have tried various options to perform a spatial left join.

Currently, we were using the S2 or H3 strategy as we need to perform LEFT JOINs in our setup (not inner joins). However, we figured out a combination of INNER JOIN and a FULL OUTER JOIN to produce a result of a LEFT JOIN by keeping high performance of Sedona spatial join.

A documentation will be updated in the PR.

[alexeyegorov]

Added a PR here: https://github.com/apache/sedona/pull/2561

[jiayuasu]

this is live here: https://sedona.apache.org/latest/api/sql/Optimizer/#spatial-left-join