Add devcontainer configuration with Dockerfile and devcontainer.json

.devcontainer/Dockerfile

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+FROM mcr.microsoft.com/devcontainers/base:bookworm
+
+# Install common CLI tooling for Helm chart development and validation.
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends \
+    ca-certificates \
+    curl \
+    git \
+    jq \
+    python3 \
+    python3-pip \
+    shellcheck \
+    yq \
+    && rm -rf /var/lib/apt/lists/*
+
+# Install the latest Helm 3 release.
+RUN curl -fsSL https://raw.githubusercontent.com/helm/helm/main/scripts/get-helm-3 | bash
+
+# Install the latest stable kubectl release.
+RUN KUBECTL_VERSION="$(curl -fsSL https://dl.k8s.io/release/stable.txt)" \
+    && curl -fsSL "https://dl.k8s.io/release/${KUBECTL_VERSION}/bin/linux/amd64/kubectl" -o /usr/local/bin/kubectl \
+    && chmod +x /usr/local/bin/kubectl
+
+# Install YAML linter via pip (available as yamllint command).
+RUN pip3 install --no-cache-dir yamllint
+
+USER vscode

.devcontainer/devcontainer.json

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+{
+  "name": "helm-charts-bookworm",
+  "runArgs": [
+    "--name=kerberos-helm-charts",
+    "--network=host"
+  ],
+  "dockerFile": "Dockerfile",
+  "mounts": [
+    "source=/var/run/docker.sock,target=/var/run/docker.sock,type=bind"
+  ],
+  "customizations": {
+    "vscode": {
+      "extensions": [
+        "GitHub.copilot",
+        "ms-azuretools.vscode-docker",
+        "ms-kubernetes-tools.vscode-kubernetes-tools",
+        "redhat.vscode-yaml"
+      ]
+    }
+  },
+  "postCreateCommand": "helm version && kubectl version --client && yamllint --version"
+}