fix: adding sentinelcommands to redis client

[sculley]

Pull Request check-list

Please make sure to review and check all of these items:

• [ x ] Does $ tox pass with this change (including linting)?
• [ x ] Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)?
• [ x ] Is the new or changed code fully tested?
• [ n/a ] Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?

Description of change

SentinalCommands have not been available to the Redis client since v3.5.3, this change re-adds the functionality to run SentinelCommands using the Redis client returned when setting up the Sentinel class.

closes #1714

[chayim]

@sculley Hope you don't mind, I updated the description, in order to get the cross-close automation.