Draft: Add support for Redis Sentinel passwords
What does this MR do?
Rename sentinelPassword to sentinelAuth to be consistent
Plus this makes it easier to add sentinel_username support later.
Related issues
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Merge Request Title and Description are up to date, accurate, and descriptive. 
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MR targeting the appropriate branch. 
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MR has a green pipeline. 
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Documentation created/updated. 
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Tests added/updated, and test plan for scenarios not covered by automated tests. 
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Equivalent MR/issue for omnibus-gitlab opened. 
Reviewers checklist
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MR has a green pipeline on https://gitlab.com/gitlab-org/charts/gitlab. 
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Consider downstream impact to the Operator, as per evaluating impact from changes to GitLab Chart.