docs(solutions): change kubelet maxPods on immutable HCS workload nodes

[chinameok]

What

Adds a How-To solution: Changing the kubelet maxPods setting on immutable infrastructure nodes (docs/en/solutions/), using HCS as the example.

Approach (S2, interim until the dedicated kubelet CRD ships)

• Existing nodes — via Machine Configuration, no reboot: node disruption policy + one-time --config-dir switch + a maxPods KubeletConfiguration drop-in, applied with DaemonReload + Restart kubelet.
• Future / rolled nodes — via the worker pool's KubeadmConfigTemplate, using a kubeadm KubeletConfiguration patch (not kubeletExtraArgs, which would become a flag and shadow the drop-in).
• Consistency — explains why re-applying the drop-in to a provider-configured node is safe (separate files, no shared ownership; keep both values identical; precedence resolves cleanly).
• Limitations — pod-CIDR ceiling on maxPods; interim method valid on ACP 4.1–4.3, migrate to the dedicated kubelet resource when it ships (objects are labeled to make that mechanical).

Notes

• ProductsVersion: 4.1.x,4.2.x,4.3.x; kind: How To; English only; no id (assigned by CI).
• yarn build passes locally.