updating devcontainer to use dockerfile to install correct version of node and adds some other helpful extensions for working in docs (#20059)

.devcontainer/Dockerfile

@@ -0,0 +1,16 @@
+# See here for image contents: https://github.com/microsoft/vscode-dev-containers/tree/v0.177.0/containers/javascript-node/.devcontainer/base.Dockerfile
+
+# [Choice] Node.js version: 16, 14, 12
+ARG VARIANT="16-buster"
+FROM mcr.microsoft.com/vscode/devcontainers/javascript-node:0-${VARIANT}
+
+# [Optional] Uncomment this section to install additional OS packages.
+# RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
+#     && apt-get -y install --no-install-recommends <your-package-list-here>
+
+# [Optional] Uncomment if you want to install an additional version of node using nvm
+# ARG EXTRA_NODE_VERSION=10
+# RUN su node -c "source /usr/local/share/nvm/nvm.sh && nvm install ${EXTRA_NODE_VERSION}"
+
+# [Optional] Uncomment if you want to install more global node modules
+# RUN su node -c "npm install -g <your-package-list-here>"

.devcontainer/devcontainer.json

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+// For format details, see https://aka.ms/devcontainer.json. For config options, see the README at:
+// https://github.com/microsoft/vscode-dev-containers/tree/v0.177.0/containers/javascript-node
+{
+	"name": "docs.github.com",
+	"build": {
+		"dockerfile": "Dockerfile",
+		// Update 'VARIANT' to pick a Node version: 12, 14, 16
+		"args": { "VARIANT": "16" }
+	},
+
+	// Set *default* container specific settings.json values on container create.
+	"settings": { 
+		"terminal.integrated.shell.linux": "/bin/bash",
+		"cSpell.language": ",en"
+	},
+
+	// Visual Studio Code extensions which help authoring for docs.github.com.
+	"extensions": [
+		"dbaeumer.vscode-eslint",
+		"sissel.shopify-liquid",
+		"davidanson.vscode-markdownlint",
+		"bierner.markdown-preview-github-styles",
+		"yzhang.markdown-all-in-one",
+		"streetsidesoftware.code-spell-checker"
+	],
+
+	// Use 'forwardPorts' to make a list of ports inside the container available locally.
+	"forwardPorts": [4000],
+
+	// Use 'postCreateCommand' to run commands after the container is created.
+	 "postCreateCommand": "npm ci && npm run build",
+
+	// Comment out connect as root instead. More info: https://aka.ms/vscode-remote/containers/non-root.
+	"remoteUser": "node"
+}