Refactor internal metrics API endpoints

[roncodes]

Summary

• Add IamMetricsController for internal IAM dashboard metrics under int/v1/metrics/iam/*.
• Add DeveloperMetricsController for internal developer dashboard metrics under int/v1/metrics/dev/*.
• Consolidate the IAM and developer dashboard metrics API work into one branch/PR.
• Keep responses aggregate-only for developer metrics and avoid exposing API key secrets, request bodies, response bodies, or webhook payload bodies.

Endpoints

• GET int/v1/metrics/iam/kpis
• GET int/v1/metrics/iam/identity-health
• GET int/v1/metrics/iam/access-coverage
• GET int/v1/metrics/iam/privileged-access
• GET int/v1/metrics/iam/policy-surface
• GET int/v1/metrics/iam/group-coverage
• GET int/v1/metrics/iam/user-lifecycle
• GET int/v1/metrics/iam/activity
• GET int/v1/metrics/dev/kpis
• GET int/v1/metrics/dev/api-traffic
• GET int/v1/metrics/dev/webhook-delivery
• GET int/v1/metrics/dev/credentials
• GET int/v1/metrics/dev/events
• GET int/v1/metrics/dev/endpoint-health
• GET int/v1/metrics/dev/activity

Companion PRs

• Developer console dashboard UI: Refactor developer dashboard widgets dev-engine#40

Validation

• php -l src/Http/Controllers/Internal/v1/IamMetricsController.php
• php -l src/Http/Controllers/Internal/v1/DeveloperMetricsController.php
• php -l src/routes.php

Documentation and API Reference Impact

• These are internal console metrics endpoints, not public Fleetbase API endpoints.
• No fleetbase/postman API spec update is expected.
• No fleetbase/fleetbase.io documentation update is expected for this internal metrics support.

Supersedes

• Supersedes the developer-only metrics API PR: Add developer dashboard metrics endpoints #220