Reduced the initial minimum number of chunks to 1 per shard for empty collections with hashed shard key

Description of Linked Ticket

Following the removal of the auto-splitter in versions >= v6.0.3, balancing does not happen anymore on number of chunks but on actual data size and the balancer is issuing moveRange commands (DOCS-15363) to atomically split+move subparts of a chunk.

Purpose of this ticket is to change the default behavior for creating/distributing chunks when sharding an empty collection with hashed shard key: one chunk per shard, in line with the decision taken also for resharding (SERVER-68050).