Raft cluster mode

**Proposal：Raft cluster mode**
Seata currently supported a stateless cluster based on DB mode, this mode need to add additional DB maintenance costs. We are exploring the Raft based clustering mode, and we hope you will be able to complete Seata Raft cluster mode with us.
• design, code, and verify the Raft cluster schema. You can use third-party component libraries.

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**Raft 集群模式**
目前Seata 支持基于DB的无状态集群模式，这种模式需要增加额外的DB维护成本。我们正在探索基于 Raft 的集群模式，希望你能够与我们一起完成 Seata 的 Raft 集群模式。
• 完成 Raft 集群模式的设计、编码和验证工作，可使用第三方组件库。

mentor: Ji Min [@slievrly ](https://github.com/slievrly), Seata project Maintainer