clarify docs about redis with sentinels

https://docs.gitlab.com/charts/advanced/external-redis/#configure-the-chart

"If you are connecting to a Redis HA cluster that has Sentinel servers running, the global.redis.host attribute needs to be set to the cluster name as specified in the sentinel.conf. Sentinel servers can be referenced using the global.redis.sentinels[0].host and global.redis.sentinels[0].port values for the --set flag. The index is zero based."

There is no "cluster name" in sentinel.conf , see https://redis.io/topics/sentinel

What is meant here? The "master-group-name" ?

I tried to create a MR, but an error occured multiple times ...