This change will result in the blocking of commands and queries conducted directly against a shard (mongod).

Docs: Customers should be made aware that they should not transition from a replica set directly to a multi-shard cluster and rather first to a single -shard cluster and connect to a router (mongos) before adding more shards. Additionally customers should be informed that they connect conduct operations when directly connected to the shard without the directShardOperations role. 

Description of Linked Ticket

The goal of this ticket is to change the behavior introduced in PM-2689 for direct operations against shards, which was that in 7.X binaries the operation was accepted but a warning was emitted. 
In 8.0 we would like to reject the operation and emit an error.