Move import admin topics to admin area of the navigation

What does this MR do and why?

As discussed in gitlab!160209 (comment 2010468383), admin topics that are limited to GitLab administrators should be navigable from the Administer area of the global navigation.

Before:

• https://docs.gitlab.com/ee/administration/settings/import_export_rate_limits.html
• https://docs.gitlab.com/ee/administration/raketasks/project_import_export.html

After:

• https://eread-move-import-admin-topics-to-admin-area-of-navigation.docs.gitlab-review.app/ee/administration/settings/import_export_rate_limits.html
• https://eread-move-import-admin-topics-to-admin-area-of-navigation.docs.gitlab-review.app/ee/administration/raketasks/project_import_export.html

Screenshots, screen recordings, or links to review app

These are strongly recommended to assist reviewers and reduce the time to merge your change.

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.