Status Page Documentation

This issue captures the work for creating a new section in GitLab's documentation for the Status Page product category. This category is going from planned to minimal in %12.9.

Proposed Documentation Outline

Title: Status Page
Sections:

• How to set-up
• Status Page layout
  • Incident List
  • Incident detail page
• How it works
  • Publishing Incidents
  • Publishing updates
  • Adding comments
  • Changing the Incident status

This new section should be located at https://docs.gitlab.com/ee/user/project/status_page/