Align kubelet resource reservations with AKS

[Copilot]

Flex nodes need AKS-compatible system and Kubernetes resource reservations so node allocatable capacity reflects host resources and pod density.

• AKS defaults
  • Calculate CPU reservation using AKS core-based tiers.
  • Calculate memory as min(20 Mi × maxPods + 50 Mi, 25% host memory).
  • Default system reservation to zero CPU and memory.
• Configuration
  • Expose systemReserved and kubeReserved overrides.
  • Propagate maxPods into kubelet configuration.
• Bootstrap
  • Use Unbounded’s kubelet configuration overlay support.
  • Document reservation defaults and overrides.

{
  "node": {
    "maxPods": 30,
    "kubelet": {
      "systemReserved": {
        "cpu": "50m",
        "memory": "100Mi"
      },
      "kubeReserved": {
        "cpu": "200m",
        "memory": "650Mi"
      }
    }
  }
}

• Fixes Set system reserve / kube reserve for node #268