feat: support upstream health checks in BackendTrafficPolicy

[AlinsRan]

Summary

This PR adds health check support to BackendTrafficPolicy, allowing users to configure active and passive health checks for upstream backends directly through the BackendTrafficPolicy resource.

Changes

New API types (api/v1alpha1/backendtrafficpolicy_types.go)

• Added HealthCheck struct with Active and Passive fields to BackendTrafficPolicySpec
• ActiveHealthCheck: configures HTTP/TCP probes with configurable interval, timeout, thresholds, and TLS settings
• PassiveHealthCheck: configures passive (observational) health monitoring with configurable thresholds
• Timeouts field uses BackendTrafficPolicyTimeouts struct (renamed json tag from timeout to timeouts for consistency)

Translation (internal/adc/translator/policies.go)

• Translates BackendTrafficPolicy.Spec.HealthCheck into APISIX upstream checks configuration
• Active health check intervals are clamped to a minimum of 1 second (APISIX requirement)
• Supports both HTTP and TCP active health check types
• Maps all threshold fields: healthy/unhealthy HTTP statuses, TCP success/failure counts

CRD regeneration

• Updated config/crd/bases/apisix.apache.org_backendtrafficpolicies.yaml with health check schema
• Updated deepcopy functions

E2E tests (test/e2e/crds/v1alpha1/backendtrafficpolicy.go)

• End-to-end tests covering:
  • Active HTTP health check configuration (interval, timeout, thresholds, HTTP path)
  • Active TCP health check configuration
  • Passive health check configuration
  • Health check deletion (verifies checks are removed from upstream)

Example

apiVersion: apisix.apache.org/v1alpha1
kind: BackendTrafficPolicy
metadata:
  name: my-policy
spec:
  targetRef:
    group: gateway.networking.k8s.io
    kind: HTTPRoute
    name: my-route
  healthCheck:
    active:
      type: HTTP
      interval: 10s
      timeout: 3s
      httpPath: /healthz
      healthy:
        httpStatuses: [200, 201]
        successes: 3
      unhealthy:
        httpStatuses: [500, 502, 503]
        httpFailures: 3