Why not support Cache use default Redis Conn Configs
current MysqlCache with redis implementation is const value
const ( defaultDatabase = 0 maxRetries = 3 idleConns = 8

https://github.com/zeromicro/go-zero/blob/eb11521655a491eaa099f3768f676825adab46cd/core/stores/redis/redisclientmanager.go#L12-L15

but max conn is very sensitive resource for redis server, does it support config in the future?
on my propose, just use RedisConfig Connection pool config is fine