Redis Health Checks do not support ACL auth_username

Title: Redis Health Checks do not support the Redis 6 ACL auth_username parameter

Description:

The only thing I was not able to handle in the previous PR #11408 is supporting auth_username for health checks. This is ok for our initial use case as we can grant the default user +ping permissions. That said, others might like this feature and I am happy to work on it.

https://github.com/envoyproxy/envoy/blob/master/source/extensions/health_checkers/redis/redis.cc#L4 is still using API V2 configuration for health checks and so I was not able to add auth_username to the proto or the impl.

I propose adding a V3 API for redis health checks that supports auth_username and make the associated changes, but I wanted to check with you on this approach before starting the work.