ci: enable caching

See https://github.com/actions/setup-node/blob/main/docs/advanced-usage.md#caching-packages-data

Part of #13

.github/workflows/generate-python-app.yml

@@ -17,6 +17,7 @@ jobs:
         uses: actions/[email protected] # https://github.com/actions/setup-node
         with:
           node-version: 16
+          cache: 'npm'
       - name: Install project dependencies
         run: npm ci # https://docs.npmjs.com/cli/v8/commands/npm-ci
       - name: Generate Python + FastAPI application