Add Partner Token Verification dashboard for Secret Detection

Summary

Adds a custom Grafana dashboard to monitor Secret Detection partner token verification API calls (AWS, GCP, Postman).

What Changed

• Added dashboards/secret-detection/partner-token-verification.dashboard.jsonnet
• Dashboard UID: sd-partner-token-verify
• Location: secret-detection folder in Grafana

What It Monitors

8 panels tracking:

• Current error rate (gauge, alerts at 10%)
• API response time P95 by partner
• Rate limit hits
• Requests per second by partner
• Success rate by partner (target: 95%+)
• Errors by type (network/rate limits/parsing)
• Network errors by partner and error class
• Rate limits by partner type

Metrics Used

• validity_check_partner_api_requests_total
• validity_check_partner_api_duration_seconds_bucket
• validity_check_rate_limit_hits_total
• validity_check_network_errors_total

Links

• Test Dashboard: https://dashboards.gitlab.net/d/secret-detection-partner/secret-detection-partner-token-verification?orgId=1&from=now-6h&to=now&timezone=browser&refresh=5m