[feature] for upsert, add uniqueness check when identifier_field_ids is set

[kevinjqliu]

Feature Request / Improvement

More context in #1665

[Fokko]

I think this should be the other way around. If you use join_cols, and you have a identifier_field_ids set, you want to make sure that the uniqueness constraint still holds.

Typing this, I'm not sure how valuable this is, this would mean that you upsert on a table by ignoring the identifier-fields (or read primary key).

[Fokko]

Thinking of it, I believe Trino fails when it finds duplicate fields on the read-path, maybe that's a better check to set. That would also cover #1666