Jk/cumulus 3320 upgrade docs

[Jkovarik]

Summary: Summary of changes

Addresses CUMULUS-3220

Changes

• Adds upgrade documentation for manual database upgrade

PR Checklist

• [ ] Update CHANGELOG
• [ ] Unit tests
• [ ] Ad-hoc testing - Deploy changes and test manually
• [ ] Integration tests

[Jkovarik]

@npauzenga thanks for the updates 🙇🏻 -- I took the changes and responded to your comments, let me know what you think!