Updates global nav for GitLab Dedicated

What does this MR do and why?

Updates global nav for GitLab Dedicated.

Related issue: https://gitlab.com/gitlab-com/gl-infra/gitlab-dedicated/team/-/issues/2724

• Link to the merge request that introduced the new page: gitlab!142762 (merged)
• Give the MR a descriptive title.
• Optional. Link to the review app showing the new page: https://lp-docs-update-dedicated-nav.docs.gitlab-review.app/ee/administration/dedicated/