Add GitHub Actions workflow to trigger docs-staging nextgen update

.github/workflows/dispatch-nextgen.yml

@@ -0,0 +1,31 @@
+name: Trigger docs-staging nextgen update
+
+on:
+  push:
+    paths-ignore:
+      - ".github/**"
+    branches:
+      - feature/preview-top-navigation
+
+jobs:
+  trigger:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+
+    steps:
+      - name: trigger docs-staging update-nextgen workflow
+        uses: actions/github-script@v7
+        with:
+          github-token: ${{ secrets.DOCS_STAGING }}
+          script: |
+            await github.rest.actions.createWorkflowDispatch({
+              owner: 'pingcap',
+              repo: 'docs-staging',
+              workflow_id: 'update-nextgen.yml',
+              ref: 'nextgen',
+              inputs: {
+                repo: 'pingcap/docs',
+                branch: 'feature/preview-top-navigation'
+              }
+            })