Add support for Sentinel specific Redis credentials

Problem

The container registry currently does not supporting using a specific password for Redis Sentinel. The existing password attribute is only used for the Redis AUTH command and not for Sentinel.

Solution

Add support for Sentinel credentials. See gitlab-org/charts/gitlab#2902 (comment 1927848248) for a summary on how this is implemented in other services. We'll need to update the registry Chart accordingly (see gitlab-org/charts/gitlab#2902 (closed)).