Add a middle layer of agents to enhance standalone IoTDB with full-fledged scalable distributed system properties

**Is your feature request related to a problem? Please describe.**

This is an enhancement feature that shall extend standalone IoTDB with scalability.
The goal of this feature is to **add a middle layer of agents to enhance standalone IoTDB with full-fledged scalable distributed system properties. **

**Describe the solution you'd like**

Would like to add a middle of stateless agents that can orchestrate a set of standalone IoTDB instances to form a full-fledged scalable distributed system.

Each of such stateless agents should at least function like [IKR](https://github.com/thulab/iotdb-kairosdb), except for 1) not supporting JSON interface at the moment; 2) support the native IoTDB session interfaces; 3) support data partitioning and sharding for the initial implementation.

**Describe alternatives you've considered**

Believe no alternatives should exist.

**Additional context**

IginX is a possible name for the agent.

首先查看独立 IoTDB 架构和链接的 IKR 项目，以了解提议的代理层。然后检查原生 IoTDB 会话接口、数据分区和分片如何在独立实例之间工作。完成这项工作需要就具备这些初始能力的无状态代理达成一致的设计并完成实现。

由索引模型根据 Issue 内容生成。