We will be preventing DDL operations performed directly against shards even in single shard clusters. This will still be bypassable via the use of the `directShardOperations` role.
Additionally, we will be adding in a new document/parameter to shards which will need to be removed if a sharded cluser backup is restored to a replica set.

Description of Linked Ticket

Summary

This project aims to improve the correctness of promotion to sharded by preventing DDL operations via direct shard connection after the promotion begins.

Motivation

The current promotion to sharded procedure allows users to run operations via both direct connections and mongoS connections while they are using a single shard. This is the source of multiple known issues which can cause data loss or metadata inconsistencies (ex. SERVER-80532). This project aims to address these issues in a simple, and quick manner by simply ensuring that once an addShard operation begins, no DDL operations are allowed via direct connection to that shard.

Documentation

Docs Update
Technical Design
Scope