support high-availability deployment for the APIServer

Currently the APIServer does not support the high availability. It just uses the built-in http protocol in brpc to serve the requests. We hope there is a solution of deploying the APIServer with high availability, and it should be integrated into our project.

The APIServer currently uses brpc's built-in HTTP. Investigate the APIServer code to understand its current deployment and request handling. Research high-availability patterns (like load balancing, leader election) suitable for brpc services. Determine how to integrate a HA solution into the existing project architecture and deployment scripts.

索引モデルが issue の本文から書いたものです。