support for redis6+ acl-only auth (in server(), auth())

[combrs]

Hello!
Now in doc I see only mention about using 'password', but it not relevant anymore: in redis6+ I can disable ' default' user and use only acl-users.
It requires to send both 'user, password' in AUTH command, but I have only

password
If your Redis server requires authentication, you can use the password attribute.

Please add support for new AUTH form for redis and sentinel (sentinel auth is separated from redis).

[joelchornik]

Hi, this pull request my solve your issue: #163