Add registration token audit event when a runner is registered

Release notes

{placeholder for release notes}

Implementation Proposal

• 1. (!67662 (merged)) Move the registration code from the REST API to a dedicated RegisterRunnerService backend service (similar to UpdateRunnerService);
• 2. Add logic to generate audit logs from the RegisterRunnerService service, as in !66234 (merged);
  • 2.1 Group/project runner registrations
  • 2.2 Instance runner registrations

Questions

• Should failed attempts to register a runner lead to an audit log entry? An example is the use of an invalid token.
  • This has been implemented

Related issues/epics

• &476 (closed)
• Add runner unregistration audit event (#349540 - closed)
• Audit CI runner event when assigning to project (#349542 - closed)
• Add runner settings changes to audit events (#8074)
• #8073 (comment 145131499)