Set up dev container

The idea is with being able to resort to the dev container the
occasional Apple Silicon user will not need to follow the extra steps in
order to be able to run tests with headless Puppeteer/Chrome.

.devcontainer/Dockerfile

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+FROM mcr.microsoft.com/devcontainers/javascript-node:0-18
+RUN apt-get update && apt-get install -y chromium xvfb
+USER node

.devcontainer/devcontainer.json

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+{
+  "name": "Node.js",
+  "build": {
+    "dockerfile": "Dockerfile"
+  },
+  "capAdd": ["SYS_ADMIN"],
+  "containerEnv": {
+    "DISPLAY": ":99",
+    "PUPPETEER_EXECUTABLE_PATH": "/usr/bin/chromium",
+    "PUPPETEER_SKIP_CHROMIUM_DOWNLOAD": "true"
+  },
+  "postStartCommand": "Xvfb :99 -ac -screen 0 1280x720x16 -nolisten tcp -nolisten unix &"
+}