Small restructure of project import global navigation

What does this MR do and why?

Brings similar topics more together and relabels the whole section.

Screenshots, screen recordings, or links to review app

• Before: https://docs.gitlab.com/ee/user/project/settings/import_export.html
• After: https://eread-small-restructure-project-import-global-navigation.docs.gitlab-review.app/ee/user/project/settings/import_export.html

Before	After

Merge request acceptance checklist

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• I have evaluated the MR acceptance checklist for this merge request.