[Feature] P2S VPNGateway support for flexnode

[wenxuan0923]

• Added new VPN Gateway component with installer, uninstaller, and operations management
• Implemented kube-proxy component for enhanced networking capabilities
• Enhanced configuration structures, logging, and utility functions
• Updated CNI setup and kubelet components for better integration

New sample config for enabling VPN gateway for flex node -> AKS node communication:

Then on top of that, user can use cilium for pod networking.

{
  "azure": {
    "subscriptionId": "xxxxxxxxxxxxx",
    "tenantId": "xxxxxxxxxxxxx",
    "cloud": "AzurePublicCloud",
    "vpnGateway": {
      "enabled": true,
      "p2sGatewayCIDR": "192.168.100.0/24",
      "podCIDR": "172.16.0.0/16",
      "vnetID": "/subscriptions/xxxxxxxxxxxxx/resourceGroups/MC_wenx-rg_wenx-edge-cluster_eastus/providers/Microsoft.Network/virtualNetworks/aks-vnet-xxxxxxx"
    },
    "arc": {
      "machineName": "edge-node",
      "tags": {
        "node-type": "edge"
      },
      "resourceGroup": "wenx-rg",
      "location": "eastus",
      "autoRoleAssignment": true
    },
    "targetCluster": {
      "resourceId": "/subscriptions/xxxxxxxxxxxxx/resourceGroups/wenx-rg/providers/Microsoft.ContainerService/managedClusters/wenx-edge-cluster",
      "location": "eastus"
    }
  },
  "kubernetes": {
    "version": "1.32.7"
  },
  "agent": {
    "logLevel": "info",
    "logDir": "/var/log/aks-flex-node"
  }
}

Then to use Cilium for pod networking, do the following (the pod CIDR must match with config above)

helm install cilium cilium/cilium \
  --version 1.16.5 \
  --namespace kube-system \
  --set operator.replicas=1 \
  --set hubble.relay.enabled=true \
  --set hubble.ui.enabled=true \
  --set routingMode=tunnel \
  --set tunnelProtocol=vxlan \
  --set autoDirectNodeRoutes=false \
  --set ipam.mode=cluster-pool \
  --set ipam.operator.clusterPoolIPv4PodCIDRList="{172.16.0.0/16}" \
  --set enableIPv4Masquerade=true \
  --set bpf.hostLegacyRouting=true \
  --set cgroup.autoMount.enabled=false \
  --set cgroup.hostRoot=/sys/fs/cgroup \
  --set bpf.autoMount.enabled=false \
  --set kubeProxyReplacement=false \
  --wait