Agent Activity Information - Backend - Iteration 1

Implements backend for #277323 (closed)

Definition of Done

• Backend supports various event types:
  • Token created - !74577 (merged)
  • [-] Token revoked - moved to #348386 (closed)
  • Agent connected - !75487 (merged)
  • [-] Agent disconnected - moved to #350269 (closed)
• Events exposed to frontend via GraphQL - !74651 (merged)
• Old events are periodically cleaned up - !75709 (merged)