Add bundlesize checks to CI

This adds a bundlesize check to the CI with very liberal tolerances for most of the chunks. It should identify egregious bundle size expansion and provide an easier path for manual comparison of master vs PRs.

Currently bundlesize doesn't work with GitHub actions out-of-the-box, but this is planned for their roadmap (and they've just got $10k from Google so I'm confident it will happen). Redux-saga seems to have this working via https://github.com/redux-saga/redux-saga/pull/1952/files.

We can revisit the settings here after the chunk hashing #1037.

.github/workflows/ci.yaml

@@ -44,3 +44,12 @@ jobs:
           node-version: ${{ matrix.node }}
       - run: npm install
       - run: npm run lint
+  bundlesize:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v1
+        with:
+          node-version: 10
+      - run: npm install
+      - run: npx bundlesize

bundlesize.config.json

@@ -0,0 +1,12 @@
+{
+  "files": [
+    {
+      "path": "./dist/auspice.bundle.js",
+      "maxSize": "180 kB"
+    },
+    {
+      "path": "./dist/auspice.chunk.*.bundle.js",
+      "maxSize": "110 kB"
+    }
+  ]
+}