set up action to publish to PyPI on release (#1270)

This is following

https://docs.github.com/en/actions/security-for-github-actions/security-hardening-your-deployments/configuring-openid-connect-in-pypi

An environment "release" has been created.

Will follow #688 as the
release process.

Author: tianyu-l

.github/workflows/release.yml

@@ -0,0 +1,49 @@
+# mostly borrowed from https://docs.github.com/en/actions/security-for-github-actions/security-hardening-your-deployments/configuring-openid-connect-in-pypi
+
+name: Publish a Release to PyPI
+
+on:
+  release:
+    types: [published]
+
+jobs:
+  release-build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.x"
+
+      - name: build release distributions
+        run: |
+          python -m pip install build
+          python -m build
+
+      - name: upload windows dists
+        uses: actions/upload-artifact@v4
+        with:
+          name: release-dists
+          path: dist/
+
+  pypi-publish:
+    runs-on: ubuntu-latest
+    needs:
+      - release-build
+    permissions:
+      id-token: write
+    environment:
+      name: release
+      url: https://pypi.org/p/torchtitan
+
+    steps:
+      - name: Retrieve release distributions
+        uses: actions/download-artifact@v4
+        with:
+          name: release-dists
+          path: dist/
+
+      - name: Publish release distributions to PyPI
+        uses: pypa/gh-action-pypi-publish@release/v1