[workflow] added trigger to build doc upon release (#2678)

.github/workflows/doc_build_after_merge.yml

+name: Build Documentation upon Release
+
+on:
+  workflow_dispatch:
+  pull_request:
+    paths:
+      - 'version.txt'
+    types:
+      - closed
+
+jobs:
+  build-doc:
+    name: Trigger Documentation Build Workflow
+    if: ( github.event_name == 'workflow_dispatch' || github.event.pull_request.merged == true ) && github.repository == 'hpcaitech/ColossalAI'
+    runs-on: ubuntu-latest
+    steps:
+      - name: trigger workflow in ColossalAI-Documentation
+        run: |
+          gh
+          curl \
+            -X POST \
+            -H "Accept: application/vnd.github+json" \
+            -H "Authorization: Bearer ${GH_TOKEN}"\
+            -H "X-GitHub-Api-Version: 2022-11-28" \
+            https://api.github.com/repos/hpcaitech/ColossalAI-Documentation/actions/workflows/deploy.yml/dispatches \
+            -d '{"ref":"main"}'
+        env:
+          GH_TOKEN: ${{secrets.DOC_REPO_TOKEN}}