chore(k8s): P2-8 doc clarifications + supply-chain pins (busybox digest, action SHAs, compose) - #766

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, azure/setup-helm@1a275c3b69536ee54be43f2070a358922e12c8d4, helm/kind-action@0025e74a8c7512023d06dc019c617aa3cf561fde. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/