Add setting to allow IN subqueries with parallel replicas

Why it matters

This feature addresses the limitation where subqueries used with the IN clause were not supported when reading from parallel replicas. Enabling this setting allows queries with IN subqueries to leverage parallel replicas, improving query performance and consistency in distributed environments.

How to use it

To enable this feature, set the parallel_replicas_allow_in_with_subquery setting to 1 in the server configuration file or at the session/query level, for example:

SET parallel_replicas_allow_in_with_subquery = 1;

This will allow subqueries in IN clauses to work with parallel replicas.