Support get addresses of all tiflash_mpp node #498
Description
TiFlash will be decoupled as ReadNode(<engine, tiflash_mpp>) and WriteNode(<engine, tiflash>).
MPPTasks will only be dispatched to ReadNodes for computation, and all region data will be stored in WriteNodes.
So client-go should support getting addresses of tiflash ReadNode to dipatch MPPTasks.
Related tidb pr: pingcap/tidb#33535