[New Rule] Elastic Endpoint and External Alerts

[spong]

Description

In support of elastic/kibana#65942 to create two new pre-packaged rules that will enable Elastic Endpoint Alerts and External Alerts to be used in investigations.

Required Info

• Eventing Sources: Elastic Endpoint and all external sources where event.kind:alert
• Target Operating Systems: All
• Platforms: All
• Target ECS Version: 1.5.0
• New fields required in ECS for this? Associated issue/PR: n/a

Optional Info

• References:
  • [SIEM][Detections] Create Endpoint/Alert pre-packaged promotion rules kibana#65942
  • [SIEM][Detections] Create Enable Rule onboarding flow kibana#65943
  • [SIEM][Detections] Create Detection Rule configuration options for mapping fields kibana#65941
  • [SIEM][Detections] Add rule.{authors, license} to the schema kibana#66317