Use new GitLab chart upgrade notes landing page

What does this MR do and why?

For: gitlab-org/gitlab#555861, and with gitlab-org/charts/gitlab!4491 (merged) merged, let's reorganise the upgrade notes section of the global navigation.

Screenshots, screen recordings, or links to review app

• Before: https://docs.gitlab.com/update/versions/
• After:
  • https://docs.gitlab.com/review-mr-1364/update/versions/
  • https://docs.gitlab.com/review-mr-1364/charts/releases/

Merge request acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this merge request.