SERVER-99299 introduced the a helper for sending aggregate command to recipient shards to get the number of documents copied from each donor shard (serially). The helper sends the aggregate command via the ShardRemote, which is an anti-pattern since the rest of the ReshardingCoordinatorService sends commands to donors and recipients via the ReshardingCoordinatorExternalState::sendCommandsToShards (i.e. sharding_ddl_util::sendAuthenticatedCommandToShards) which uses async_rpc::sendCommand and sends the commands in parallel.

We should make the helper use ReshardingCoordinatorExternalState::sendCommandsToShards. It currently doesn't return the command responses but that can be changed.