Reduce the number of operations written to the etcd storage in a single transaction

[ZuLiangWang]

In current etcd storage implementation, it will write and query the metadata of the cluster and shard with transaction containing multiple operations, like this:

	for _, shardView := range req.ShardViews {
		opCreateShardTopologiesAndLatestVersion = append(opCreateShardTopologiesAndLatestVersion, clientv3.OpPut(key, string(value)), clientv3.OpPut(latestVersionKey, fmtID(shardView.Version)))
	}
	resp, err := s.client.Txn(ctx).
		If(keysMissing...).
		Then(opCreateShardTopologiesAndLatestVersion...).
		Commit()

An error occurs when the number of operations exceeds the maximum limit of etcd. Try to optimize these writing methods to reduce the number of operations under the same data volume.