feat(loadbalancer): add healthCheckNodePort opt-in support

[aslafy-z]

Description

This PR extends the service.beta.kubernetes.io/scw-loadbalancer-health-check-port annotation (introduced in #195) with support for automatic detection of Kubernetes' healthCheckNodePort.

Problem

When using externalTrafficPolicy: Local, kube-proxy (or cilium) allocates a dedicated spec.healthCheckNodePort on each node specifically for load balancer health probes. While #195 added the ability to manually specify a health check port, users still had to look up and hardcode the healthCheckNodePort value.

Fixes #192
Depends on #195

Solution

Added support for the special value "auto" which:

• When externalTrafficPolicy: Local and spec.healthCheckNodePort is set → uses healthCheckNodePort
• Otherwise → falls back to nodePort (default behavior)

This aligns with native Kubernetes LoadBalancer health check behavior and enables seamless client source IP preservation.

Example Usage

apiVersion: v1
kind: Service
metadata:
  name: my-service
  annotations:
    # Automatic detection: uses healthCheckNodePort when available
    service.beta.kubernetes.io/scw-loadbalancer-health-check-port: "auto"
spec:
  type: LoadBalancer
  externalTrafficPolicy: Local 
  ports:
    - port: 80
      targetPort: 8080

Per-port configuration is also supported:

service.beta.kubernetes.io/scw-loadbalancer-health-check-port: "80:auto;443:31234"

Future Work

In the next major release, "auto" will become the default behavior.