Feat/mongodb secret connection

[uzmargomez]

What this PR does / why we need it:
Allows MongoDB auth string to come from secret

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Verify the work you plan to merge addresses an existing issue (If not, open a new one) (required)
• Check your branch with helm lint (required)
• Update version in Chart.yaml according semver rules (required)
• Substitute annotations section in Chart.yaml annotating implementations (useful for Artifecthub changelog) (required)
• Update chart README using helm-docs (required)

Which issue(s) this PR fixes:

Fixes #372

Special notes for your reviewer: