Add setup-node to OpenAPI decorate workflow (#20469)

* Add setup-node to OpenAPI decorate workflow

* Add description of the workflow

.github/workflows/openapi-decorate.yml

@@ -1,8 +1,8 @@
 name: OpenAPI generate decorated schema files
 
-# **What it does**:
-# **Why we have it**:
-# **Who does it impact**:
+# **What it does**: On 'Update OpenAPI Descriptions' PRs opened by github-openapi-bot, this workflow runs the script to generate the decorated OpenAPI files and commit them to the PR.
+# **Why we have it**: So we can consume OpenAPI changes, decorate them, and publish them to the REST API docs.
+# **Who does it impact**: Anyone making OpenAPI changes in `github/github`, and wanting to get them published on the docs site.
 
 on:
   workflow_dispatch:
@@ -21,6 +21,12 @@ jobs:
       - name: Checkout repository code
         uses: actions/checkout@5a4ac9002d0be2fb38bd78e4b4dbde5606d7042f
 
+      - name: Setup node
+        uses: actions/setup-node@38d90ce44d5275ad62cc48384b3d8a58c500bb5f
+        with:
+          node-version: 16.x
+          cache: npm
+
       - name: Install dependencies
         run: npm ci