Add changelog.txt update workflow (woocommerce#34554)

.github/workflows/post-release.yml

@@ -0,0 +1,68 @@
+name: Run post release processes
+on: 
+  release:
+    types: [released]
+
+env:
+    GIT_COMMITTER_NAME: 'WooCommerce Bot'
+    GIT_COMMITTER_EMAIL: 'no-reply@woocommerce.com'
+    GIT_AUTHOR_NAME: 'WooCommerce Bot'
+    GIT_AUTHOR_EMAIL: 'no-reply@woocommerce.com'
+
+jobs:
+  update-changelog-in-trunk:
+    name: Update changelog in trunk
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v3
+      - name: Get tag name
+        id: tag
+        uses: actions/github-script@v6
+        with:
+          script: |
+            const tag = ${{ toJSON( github.event.release.tag_name ) }}
+
+            console.log( `::set-output name=tag::release/${ tag.substring( 0, 3 ) }` )
+
+      - name: Git fetch trunk branch
+        run: git fetch origin trunk
+
+      - name: Copy changelog.txt to vm root
+        run: cp changelog.txt ../../changelog.txt
+
+      - name: Switch to trunk branch
+        run: git checkout trunk
+
+      - name: Create a new branch based on trunk
+        run: git checkout -b update/changelog-from-release-${{ github.event.release.tag_name }}
+
+      - name: Copy saved changelog.txt to monorepo
+        run: cp ../../changelog.txt ./changelog.txt
+
+      - name: Commit changes
+        run: git commit -am "Update changelog.txt from release ${{ github.event.release.tag_name }}"
+
+      - name: Push branch up
+        run: git push origin update/changelog-from-release-${{ github.event.release.tag_name }}
+
+      - name: Create the PR
+        uses: actions/github-script@v6
+        with:
+          script: |
+            const body = "This PR updates the changelog.txt based on the latest release: ${{ github.event.release.tag_name }}"
+
+            const pr = await github.rest.pulls.create({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              title: "Update changelog.txt from release ${{ github.event.release.tag_name }}",
+              head: "update/changelog-from-release-${{ github.event.release.tag_name }}",
+              base: "trunk",
+              body: body
+            })
+
+            const prCreated = await github.rest.pulls.requestReviewers({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              pull_number: pr.data.number,
+              reviewers: ["${{ github.event.release.author.login }}"]
+            })