In catalog shard implementation the ShardingCatalogManager::addShard() the Shard connection to the shard to be added should be always remote.

The reason for this is that in the catalog shard implementation the ShardingCatalogManager can run at the same server as the shard we are trying to add. The commands sent to that shard require majority concerns and probably other stuff not supported by a direct client. Just always force a remote shard connection by adding a shard registry createRemoteConnection() method.

For non catalog shard mode this is no-op because the shard is always remote.