Support snapshot_properties in upsert operation

[ksoullpwk]

Feature Request / Improvement

I see the other operations (like append, overwrite, delete, etc) has already supported snapshot_properties in arguments. I guess upsert operation should be able to pass this argument too since it internally calls append and overwrite which has supported.

[ksoullpwk]

One question after looking into the code, should the upsert operation produce 1 snapshot or 2 snapshots?

I looked into the Spark integration test in iceberg repo and found that Spark will produce only 1 snapshot after running merge into. But from iceberg-python, the upsert operation might run both overwrite and append and produce 2 snapshots.