[oracle] Add alerting service integration with PagerDuty or webhook

[Otaiki1]

Summary

oracle/src/health/alerting.service.ts exists but likely only logs alerts internally. Operators need to receive external alerts (PagerDuty, Slack webhook, or email) when critical conditions occur: circuit OPEN, DLQ threshold exceeded, or key rotation failure.

What to do

1. Add ALERT_WEBHOOK_URL and ALERT_PAGERDUTY_KEY to the oracle env schema (both optional).
2. In AlertingService.sendAlert(level, message, context):
   • If ALERT_WEBHOOK_URL is set, POST a JSON payload to the URL (Slack-compatible format).
   • If ALERT_PAGERDUTY_KEY is set, use PagerDuty's Events API v2.
3. Trigger alerts for: circuit breaker OPEN, DLQ depth > configurable threshold, VRF key unavailable.
4. Include oracle_id, raffle_id (if applicable), and severity in the alert payload.
5. Write a unit test mocking the HTTP client to assert alert payloads are correctly formed.

Acceptance criteria

• Setting ALERT_WEBHOOK_URL causes alerts to POST to that URL when the circuit opens.
• Alert payload contains enough context to diagnose the issue without SSH access.

[Kingvic300]

@Kingvic300 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I would love to work on this

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