devops: add NPM publishing (#4)

Requires the `NPM_TOKEN` secret to be set.

.github/workflows/publish.yml

@@ -0,0 +1,18 @@
+name: Publish
+on:
+  release:
+    types: [published]
+jobs:
+  publish-npm:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 18
+          registry-url: https://registry.npmjs.org/
+      - run: npm ci
+      - run: npm run build
+      - run: npm publish
+        env:
+          NODE_AUTH_TOKEN: ${{secrets.NPM_TOKEN}}