Added basic Redis Sentinel support

Closes #1501 (closed)

I have a 3 node redis cluster running in the K8S environment with Sentinel containers in each Pod. I was having some issues with the YAML generation, but that has been resolved and the chart has been deploying for a while.

Most of the config files get the Sentinel information, but there are two files that I am still tracking down how to correctly create the config entries for Sentinel servers. The outstanding config files are

• gitlab-exporter.yml for the gitlab-exporter chart
• mail_room.yml for the mailroom chart

I am making the assumption that if the Sentinel servers are specified, that the Redis master server will not be listed. So the above need to also be updated. To my understanding one can not take the connection information for a Sentinel server and list it as the normal Redis server. There seems to be a few differences to prevent this.