SPM-3398 enables users to drop the shard key index for a collection that is sharded on a hashed shard key since the shard key index is only required by chunk migrations and range deletions, and hashed sharded collections generally do not require chunk migrations since hash sharding already provides good data distribution and customers in 5.0+ can always use resharding to redistribute their data. However, SPM-3398 doesn't allow users to have a hashed sharded collection without the shard key index from the start. That is, they need to create the index, shard the collection and then drop it. The goal of this ticket is to explore making the index optional upon sharding the collection.