Implement ledger metrics for observability and add tests for Ruby packages endpoints

- Added `LedgerMetrics` class to record write latency and total events for ledger operations.
- Created comprehensive tests for Ruby packages endpoints, covering scenarios for missing inventory, successful retrieval, and identifier handling.
- Introduced `TestSurfaceSecretsScope` for managing environment variables during tests.
- Developed `ProvenanceMongoExtensions` for attaching DSSE provenance and trust information to event documents.
- Implemented `EventProvenanceWriter` and `EventWriter` classes for managing event provenance in MongoDB.
- Established MongoDB indexes for efficient querying of events based on provenance and trust.
- Added models and JSON parsing logic for DSSE provenance and trust information.

offline/notifier/templates/attestation/tmpl-attest-key-rotation.webhook.en-us.template.json

@@ -0,0 +1,16 @@
+{
+  "schemaVersion": "notify.template@1",
+  "templateId": "tmpl-attest-key-rotation-webhook-en-us",
+  "tenantId": "bootstrap",
+  "channelType": "webhook",
+  "key": "tmpl-attest-key-rotation",
+  "locale": "en-us",
+  "renderMode": "json",
+  "format": "webhook",
+  "description": "Webhook payload for attestation key rotation/revocation events.",
+  "body": "{\n  \"event\": \"authority.keys.rotated\",\n  \"tenantId\": \"{{event.tenant}}\",\n  \"batchId\": \"{{payload.rotation.batchId}}\",\n  \"executedAt\": \"{{payload.rotation.executedAt}}\",\n  \"impactedServices\": \"{{payload.rotation.impactedServices}}\",\n  \"reason\": \"{{payload.rotation.reason}}\",\n  \"links\": {\n    \"docs\": \"{{payload.links.docs}}\",\n    \"console\": \"{{payload.links.console}}\"\n  }\n}\n",
+  "metadata": {
+    "author": "notifications-bootstrap",
+    "version": "2025-11-12"
+  }
+}