Add terms of service to left nav

Add navigation item to global navigation

The following page is missing from the left nav: https://docs.gitlab.com/ee/user/admin_area/settings/terms.html

It's an Admin Area setting, so placing it under Configuration and Admin Area.

Preview: https://kpaizee-main-patch-67708.docs.gitlab-review.app/ee/user/admin_area/settings/terms.html

Related issue: technical-writing#712 (closed)