Add compatibility tests for $group pushdown behavior

This work adds a JS test suite that compares the behavior between execution of $group in the classic engine vs $group pushdown into sbe. We could consider a randomized testing approach for data generation, not for queries. Randomized queries makes it too hard to investigate a failure.

The main goal here is to expose incompatible behaviors between the behaviors of $group in classic engine and ones of $group in SBE as soon as possible and make them easy to investigate.