Begin to reflect refined information architecture in global nav for Git

What does this MR do and why?

A companion to: gitlab!148926 (merged), and discussed in: gitlab#451591 (comment 1852144292).

Make sure that the pages in the navigation reflect the order they should be read as a user that is new to Git.

Screenshots, screen recordings, or links to review app

• Before: https://docs.gitlab.com/ee/topics/git/
• After: https://eread-reflect-refined-info-arch-in-git-global-nav.docs.gitlab-review.app/ee/topics/git/

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Configure a local GitLab Docs environment: https://gitlab.com/gitlab-org/gitlab-docs/-/blob/main/doc/setup.md.

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.