Update docs with required permissions when using restrictive sentinel permissions

[molteber]

I'm using restrictive permissions for users when they connect to our sentinel instances to get our primary redis instance.

I set the permissions to what they mentioned in https://redis.io/docs/management/sentinel/#sentinel-access-control-list-authentication

-@all +auth +client|getname +client|id +client|setname +command +hello +ping +role +sentinel|get-master-addr-by-name +sentinel|master +sentinel|myid +sentinel|replicas +sentinel|sentinels

Using only this, one get the error

StackExchange.Redis.RedisConnectionException: Sentinel: The ConnectionMultiplexer is not a Sentinel connection. Detected as: Standalone

The current documentation mentions sort of that required permissions for sentinel is the whole sentinel command namespace, sort of. But I wanted to be able to use the restrictive permissions redis suggests themselves. So I started digging for what permissions you actually require, because the application works fine when the user is not restricted.

After a digging for a while I found the following: https://github.com/StackExchange/StackExchange.Redis/blob/main/src/StackExchange.Redis/ServerEndPoint.cs#L407-L412 I tried adding +sentinel|masters, and now it worked!

Not sure if this is the only sentinel command it requires to detect it as a sentinel server, but it think it will be useful to specify the permissions required to detect a sentinel server in the documentation