To convert a standalone replica set to a sharded cluster, we currently require users start a fresh config server, restart every replica set node with the --shardsvr command line option, then add the shard to the cluster. If a user wants to convert to a one shard cluster with a colocated config server shard (ie a catalog shard), they should be able to restart the standalone set's nodes with the --configsvr command line option, which is currently not allowed.