Open and resolve PagerDuty incidents

[tomschlick]

Summary

• Send Events API v2 trigger events when a monitor goes down and resolve events with the same dedup key when it recovers, so PagerDuty opens and closes the incident.
• Reject integration keys that are not 32 hexadecimal characters, strip credentials from the affected system, and include the failure details plus a link back to the monitor.
• Channel tests trigger and then resolve, and throttled or 5xx responses are retried.

Test plan

• Save a PagerDuty channel with a real 32-character Events API v2 integration key, and confirm a short or non-hex key is rejected.
• Send a test notification and confirm the incident opens and then resolves.
• Fail a monitor past its threshold and confirm one incident opens; recover it and confirm that incident resolves.
• Confirm a database monitor alert does not include the connection password.