Update test plan per latest discussion

Related to #451 (closed)

Closes #476 (closed)

• Add new test areas as discussed by the team
• Remove geo automated test runs since we can't run them on staging
• Add test owners for Create an issue from email and Issue Board

Reprioritized tests

• During blackout
  • Repository Operations
  • Uploads
  • Artifacts
  • Basic API tests
  • Container Registry integration
  • Some basic validation for Webhooks
  • Issue boards
  • CI/CD Workflow (Basic flow)
  • GitLab Service Desk (PRODUCTION ONLY)
  • AlertManager Alerts
• After blackout
  • CI/CD Workflow (Advanced flow)
  • Email
  • Wiki Operations
  • Pages
  • Mirror
  • Backups
  • File locking
  • CI/CD for external repo
  • CI/CD for GitHub
  • Kubernetes monitoring
  • AutoDevOps workflow - needs owner
  • Integrating Kubernetes clusters - needs owner
  • Canary deployments needs owner
  • Multi-project pipelines needs owner