Add documentation to `Redis` and `RedisCluster` that we allow `user` option

[boesing]

Feature Request

Q	A
New Feature	yes

Summary

With laminas/laminas-cache-storage-adapter-redis#92, the Redis implementation allows user option to be passed so that users can authenticate against redis with a user/password combination.

With laminas/laminas-cache-storage-adapter-redis#122, the RedisCluster implementation will allow user option to be passed.

Since documentation is still not available from the adapters itself, we have to add these here. (cc @froschdesign)