feat(loadbalancer): add health check port annotation

[aslafy-z]

Fixes #194
Partially addresses #192

Summary

This PR introduces a new annotation service.beta.kubernetes.io/scw-loadbalancer-health-check-port that allows users to explicitly define the port used for health checks on Scaleway Load Balancers.

Motivation

The Scaleway CCM currently determines the LoadBalancer health check port based on the per-port nodePort. However, there is no simple way to force a specific port for the health check, which is limiting in several use cases:

• Legacy probes on fixed ports
• Constrained firewall rules
• Fixed monitoring pipelines
• Using spec.healthCheckNodePort with externalTrafficPolicy: Local

Changes

• New annotation: service.beta.kubernetes.io/scw-loadbalancer-health-check-port
  • Single port for all backends: 18080
  • Per-port configuration: 80:10080;443:10443
  • Mixed with default fallback: 80,8080:10080;9090 (port 8888 would use 9090)
  • Valid port range: 1-65535
  • Falls back to NodePort when not set or no match

Usage Examples

apiVersion: v1
kind: Service
metadata:
  name: my-service
  annotations:
    service.beta.kubernetes.io/scw-loadbalancer-health-check-port: "30021"
spec:
  type: LoadBalancer
  externalTrafficPolicy: Local
  healthCheckNodePort: 30021  # manual defined to ensure the value stays stable 
  ports:
    - port: 80
      targetPort: 8080

apiVersion: v1
kind: Service
metadata:
  name: my-service
  annotations:
    # Per-port configuration
    service.beta.kubernetes.io/scw-loadbalancer-health-check-port: "80:10080;443:10443"
spec:
  type: LoadBalancer
  ports:
    - port: 80
      targetPort: 8080
    - port: 443
      targetPort: 8443

apiVersion: v1
kind: Service
metadata:
  name: my-service
  annotations:
    # Mixed: specific ports + default fallback
    # port 80 or 8080 → 10080, all others → 9090
    service.beta.kubernetes.io/scw-loadbalancer-health-check-port: "80,8080:10080;9090"
spec:
  type: LoadBalancer
  ports:
    - port: 80
    - port: 443
    - port: 8080

Testing

• Added unit tests covering:
  • Default behavior (no annotation, returns nodePort)
  • Minimum valid port (1)
  • Maximum valid port (65535)
  • Error cases: port too low (0), port too high (65536), negative port, non-numeric value

Future Work

For full resolution of #192, a follow-up PR could automatically detect and use spec.healthCheckNodePort when externalTrafficPolicy: Local is set, without requiring manual annotation.