[workflow] added workflow to release to pypi upon version change (#2320)

* [workflow] added workflow to release to pypi upon version change

* polish code

* polish code

* polish code

.github/workflows/release_pypi.yml

+name: Publish to PyPI
+
+on:
+  workflow_dispatch:
+  pull_request:
+    paths:
+      - 'version.txt'
+    types:
+      - closed
+
+jobs:
+  build-n-publish:
+    if: github.event_name == "workflow_dispatch" || github.repository == 'hpcaitech/ColossalAI' && github.event.pull_request.merged == true && github.base_ref == 'main' 
+    name: Build and publish Python 🐍 distributions 📦 to PyPI
+    runs-on: ubuntu-latest
+    timeout-minutes: 20
+    steps:
+    - uses: actions/checkout@v2
+
+    - uses: actions/setup-python@v2
+        with:
+          python-version: '3.8.14'
+
+    - run: python setup.py sdist build
+    
+    # publish to PyPI if executed on the main branch
+    - name: Publish package to PyPI
+      uses: pypa/gh-action-pypi-publish@release/v1
+      with:
+        user: __token__
+        password: ${{ secrets.PYPI_API_TOKEN }}
+        verbose: true