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.

Start by reviewing the standalone IoTDB architecture and the linked IKR project to understand the proposed agent layer. Then examine how native IoTDB session interfaces, data partitioning, and sharding would need to work across standalone instances. Done would require an agreed design and implementation of the stateless agents with those initial capabilities.

Written by the indexing model from the issue text.