Update Plan stage pages with 14.0 Admin Area access info

Proposal

Details about this issue are in: #333265 (closed)

Wording to use for accessing Admin Area features in product docs are located in the Style Guide at: https://docs.gitlab.com/ee/development/documentation/styleguide/index.html#how-to-document-the-menus

• /user/project/issues/design_management.md
• /user/admin_area/settings/email.md
• /user/admin_area/settings/rate_limit_on_issues_creation.md
• /user/admin_area/settings/rate_limit_on_notes_creation.md
• /user/project/description_templates.md
• /user/project/time_tracking.md

Related to #333265 (closed)