While adding new fields to configure change stream aggregation pipelines (i.e. $changeStream) we figured out that additional fields will influence the query shapes (and thus the query shape hashes) of such pipelines. All new fields for change stream pipelines thus have to be marked as optional, with no default values in the IDL.

This wasn't covered yet by existing tests, so it will be useful to add explicit tests that verify the query shapes and query shape hashes for change stream aggregation pipelines.