Add gh-pages workflow

Add devcontainer upddate package.json to reflect the requirements:

* node 8 due to rollup-plugin-commonjs error with node >= 10:
  "The argument 'path' must be a string or Uint8Array without null bytes"
* npm >= 4 due to npm/cli#681

.devcontainer/Dockerfile

@@ -0,0 +1,14 @@
+# See here for image contents: https://github.com/microsoft/vscode-dev-containers/tree/v0.238.0/containers/ubuntu/.devcontainer/base.Dockerfile
+
+# [Choice] Ubuntu version (use ubuntu-22.04 or ubuntu-18.04 on local arm64/Apple Silicon): ubuntu-22.04, ubuntu-20.04, ubuntu-18.04
+ARG VARIANT="ubuntu-18.04"
+FROM mcr.microsoft.com/vscode/devcontainers/base:0-${VARIANT}
+
+# need node <10, but npm newer than 3.x to work around
+# install newer npm to work https://github.com/npm/cli/issues/681
+ RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
+     && apt-get -y install --no-install-recommends npm \
+     && npm install -g npm@6 \
+     && rm -rf /var/lib/apt/lists/*
+
+

.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/v0.238.0/containers/ubuntu
+{
+	"name": "Ubuntu",
+	"build": {
+		"dockerfile": "Dockerfile",
+		// Update 'VARIANT' to pick an Ubuntu version: jammy / ubuntu-22.04, focal / ubuntu-20.04, bionic /ubuntu-18.04
+		// Use ubuntu-22.04 or ubuntu-18.04 on local arm64/Apple Silicon.
+		"args": { "VARIANT": "ubuntu-18.04" }
+	},
+
+	// Use 'forwardPorts' to make a list of ports inside the container available locally.
+	// "forwardPorts": [],
+
+	// Use 'postCreateCommand' to run commands after the container is created.
+	// "postCreateCommand": "uname -a",
+
+	// Comment out to connect as root instead. More info: https://aka.ms/vscode-remote/containers/non-root.
+	"remoteUser": "vscode"
+}

.github/workflows/gh-pages.yml

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+on:
+  push:
+    branches:
+      - 'pin-node-8'
+
+jobs:
+  github-pages:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          submodules: recursive
+
+      - uses: actions/setup-node@v3
+        with:
+          node-version: 8
+
+      - run: npm ci
+      - run: npm run build
+      - run: mkdir public && mv build cmap.json config data images index.html public/
+
+      - uses: peaceiris/actions-gh-pages@v3
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          publish_dir: ./public
+          publish_branch: 'legumfederation.github.io/cmap-js'