Update upgrade.md to ensure that orphanage resources are cleaned up

What does this MR do?

Makes changes to include extra steps during helm upgrades. Redis resources aren't always cleaned up with the stateful delete command this can lead to other pods failing.

Related issues

Discovered during an customer upgrade: https://gitlab.com/gitlab-com/customer-success/professional-services-group/professional-services-delivery/gitlab-professional-services/Mattel-PS-Upgrade-to-16-x-and-Migrate-to-SaaS/SOW-2506/-/issues/incident/20

Author checklist

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Required

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• Merge Request Title and Description are up to date, accurate, and descriptive.
• MR targeting the appropriate branch.
• MR has a green pipeline.
• Documentation created/updated.
• Tests added/updated, and test plan for scenarios not covered by automated tests.
• Equivalent MR/issue for omnibus-gitlab opened.

Reviewers checklist

• MR has a green pipeline on https://gitlab.com/gitlab-org/charts/gitlab.
• Consider downstream impact to the Operator, as per evaluating impact from changes to GitLab Chart.