redis cluster support

**Is your feature request related to a problem? (你需要的功能是否与某个问题有关?)**
no

**Describe the solution you'd like (描述你期望的解决方法)**
希望 redis的客户端可以支持 cluster 和 sentinel 的连接方式

**Describe alternatives you've considered (描述你想到的折衷方案)**
或者内置 redis-plus-plus 库

**Additional context/screenshots (更多上下文/截图)**

No implementation files, tests, or entry points are named. Start by locating brpc's Redis client integration and documenting how connections are currently created, then compare the requirements for Redis Cluster and Sentinel support. Done means both connection modes are supported with clear configuration and coverage for their distinct behaviors.

Written by the indexing model from the issue text.