Add new Geo sites API page to global nav

What does this MR do and why?

Companion to: gitlab!115654 (merged), to add new page to global navigation.

CC @brodock @msolodovnik-ext, @axil

Screenshots, screen recordings, or links to review app

• https://eread-add-new-geo-sites-api-page-to-global-nav.docs.gitlab-review.app/ee/api/geo_sites.html

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.