"Upgrading Jenkins X" docs audit

[jha-cloudbees]

To Dev/Contributor: Assign to yourself to "adopt" this update.

https://jenkins-x.io/docs/guides/managing-jx/common-tasks/upgrade-jx/ https://github.com/jenkins-x/jx-docs/edit/master/content/en/docs/guides/managing-jx/common-tasks/upgrade-jx.md

Content audit checklist:

• [ ] Content needs review and/or update
• [ ] Content is fine, no changes needed
• [ ] Content needs to be archived
• [ ] Content needs to be removed