TELESTION-447 Add API reference

Fix GH docs workflow, attempt No. 2 (setting up pnpm)

.github/workflows/docs.yml

@@ -12,10 +12,12 @@ jobs:
     steps:
       - name: Checkout main
         uses: actions/checkout@v2
-      - name: Setup Node/pnpm
+      - name: Setup Node
         uses: actions/setup-node@v2
         with:
           node-version: 21
+      - name: Install pnpm
+        uses: pnpm/action-setup@v2
       - name: Build API Reference for frontend-react
         working-directory: frontend-react
         run: |