Add metadata to Plan pages

What does this MR do?

Related to #216290 (closed)

groupproject management pages to be updated

---
stage: Plan
group: Project Management
info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
---

Issue Tracking

• https://docs.gitlab.com/ee/administration/incoming_email.html
• https://docs.gitlab.com/ee/development/file_storage.html
• https://docs.gitlab.com/ee/integration/jira_development_panel.html
• https://docs.gitlab.com/ee/user/admin_area/settings/email.html
• https://docs.gitlab.com/ee/user/award_emojis.html
• https://docs.gitlab.com/ee/user/discussions/index.html
• https://docs.gitlab.com/ee/user/markdown.html
• https://docs.gitlab.com/ee/user/profile/notifications.html
• https://docs.gitlab.com/ee/user/project/bulk_editing.html
• https://docs.gitlab.com/ee/user/project/description_templates.html
• https://docs.gitlab.com/ee/user/project/import/jira.html
• https://docs.gitlab.com/ee/user/project/integrations/jira.html
• https://docs.gitlab.com/ee/user/project/issues/index.html
• https://docs.gitlab.com/ee/user/project/issue_board.html
• https://docs.gitlab.com/ee/user/project/issues/confidential_issues.html
• https://docs.gitlab.com/ee/user/project/issues/due_dates.html
• https://docs.gitlab.com/ee/user/project/issues/issue_weight.html
• https://docs.gitlab.com/ee/user/project/issues/related_issues.html
• https://docs.gitlab.com/ee/user/project/labels.html
• https://docs.gitlab.com/ee/user/project/milestones/index.html
• https://docs.gitlab.com/ee/user/project/quick_actions.html
• https://docs.gitlab.com/ee/user/todos.html

Not in TOC - being added #218665 (closed)

• https://docs.gitlab.com/ee/user/project/issues/associate_zoom_meeting.html
• https://docs.gitlab.com/ee/user/project/issues/crosslinking_issues.html
• https://docs.gitlab.com/ee/user/project/issues/issue_data_and_actions.html
• https://docs.gitlab.com/ee/user/project/issues/managing_issues.html
• https://docs.gitlab.com/ee/user/project/issues/multiple_assignees_for_issues.html
• https://docs.gitlab.com/ee/user/project/issues/sorting_issue_lists.html
• https://docs.gitlab.com/ee/user/project/milestones/burndown_charts.html

Kanban Boards

• https://docs.gitlab.com/ee/user/project/issue_board.html (already in Issue Tracking too)

Time Tracking

• https://docs.gitlab.com/ee/user/project/time_tracking.html

API pages

• https://docs.gitlab.com/ee/api/award_emoji.html
• https://docs.gitlab.com/ee/api/boards.html
• https://docs.gitlab.com/ee/api/discussions.html
• https://docs.gitlab.com/ee/api/group_boards.html
• https://docs.gitlab.com/ee/api/group_labels.html
• https://docs.gitlab.com/ee/api/group_milestones.html
• https://docs.gitlab.com/ee/api/issues_statistics.html
• https://docs.gitlab.com/ee/api/issues.html
• https://docs.gitlab.com/ee/api/labels.html
• https://docs.gitlab.com/ee/api/markdown.html
• https://docs.gitlab.com/ee/api/milestones.html
• https://docs.gitlab.com/ee/api/projects.html
• https://docs.gitlab.com/ee/api/resource_milestone_events.html (will add in !31720 (merged))
• https://docs.gitlab.com/ee/api/todos.html

~"group::portfolio management" pages to be updated

---
stage: Plan
group: Portfolio Management
info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
---

Epics

• https://docs.gitlab.com/ee/user/group/epics/index.html
• https://docs.gitlab.com/ee/user/group/epics/manage_epics.html

Roadmaps

• https://docs.gitlab.com/ee/user/group/roadmap/index.html

API pages

• https://docs.gitlab.com/ee/api/epic_issues.html
• https://docs.gitlab.com/ee/api/epics.html

~"group::certify" pages to be updated

---
stage: Plan
group: Certify
info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
---

Service Desk

• https://docs.gitlab.com/ee/user/project/service_desk.html

Requirements Management

• https://docs.gitlab.com/ee/user/project/requirements/index.html