Add new GitLab 15 and GitLab 14 changes items to global navigation

What does this MR do and why?

Adds new navigation items for files created in: gitlab!129896 (merged).

Contributes to: technical-writing#843 (closed).

Review app:

• https://eread-add-new-gitlab-changes-items-to-global-nav.docs.gitlab-review.app/ee/update/versions/gitlab_15_changes.html
• https://eread-add-new-gitlab-changes-items-to-global-nav.docs.gitlab-review.app/ee/update/versions/gitlab_14_changes.html

CC @axil