Add kubernetes-deployment: probes, shutdown, JVM ergonomics, HPA

Companion code for "Deploying Spring Boot 4 on Kubernetes: Probes, Graceful
Shutdown, Limits and JVM Ergonomics". A dependency outage under three
probe-group setups, a rolling restart under load four ways (three runs
each), the JVM's ergonomic choices for nine pod shapes, one GC-heavy load
under five CPU limits with throttling counters, and an HPA driven by a
Micrometer gauge through prometheus-adapter. Measured on k3s v1.36.4.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01C3TETMrqVUWeFkNtz3Jbo3

kubernetes-deployment/scripts/env.sh

@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+MODULE_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+OUT="$MODULE_DIR/docs/output"
+NS=demo
+IMAGE="${IMAGE:-sbd/k8s-demo:1}"
+mkdir -p "$OUT"
+export KUBECONFIG="${KUBECONFIG:-/etc/rancher/k3s/k3s.yaml}"
+# Run a one-off pod from the app image with an arbitrary command and resources; print its logs.
+#   oneoff <name> '<resources-json>' <command...>
+oneoff() {
+  local name="$1" resources="$2"; shift 2
+  local cmd; cmd=$(printf '"%s",' "$@"); cmd="[${cmd%,}]"
+  kubectl -n "$NS" delete pod "$name" --ignore-not-found --wait=true > /dev/null
+  kubectl -n "$NS" apply -f - > /dev/null <<YAML
+apiVersion: v1
+kind: Pod
+metadata: {name: $name, namespace: $NS, labels: {role: oneoff}}
+spec:
+  restartPolicy: Never
+  containers:
+    - name: app
+      image: $IMAGE
+      imagePullPolicy: Never
+      command: $cmd
+      resources: $resources
+YAML
+  kubectl -n "$NS" wait --for=jsonpath='{.status.phase}'=Succeeded "pod/$name" --timeout=120s > /dev/null
+  kubectl -n "$NS" logs "$name"
+  kubectl -n "$NS" delete pod "$name" --wait=false > /dev/null
+}