Detections and alerts section

[nastasha-solomon]

• Added the remaining content that was missing from the "Detections and alerts" section. Content can be found under Solutions and use cases > Security > Detections and alerts
• Removed raw migrated content files (ESS and Serverless) and unused Serverless image files for a few pages. The remaining unused content will be removed in a separate PR.

Preview:

• Detections and alerts
  • Detections requirements
  • Using logsdb index mode with Elastic Security
  • About detection rules
  • Create a detection rule
    • Launch Timeline from investigation guides
  • Install and manage Elastic prebuilt rules
  • Manage detection rules
  • Manage detection alerts
    • Visualize detection alerts
    • View detection alert details
    • Add detection alerts to cases
    • Suppress detection alerts
  • Reduce notifications and alerts
  • Query alert indices
  • Tune detection rules

[nastasha-solomon]

This PR is no longer needed. #463 takes care of these pages.