GHA for generating the post-release pull request (#6449)

.github/scripts/get-prior-version.sh

@@ -0,0 +1,22 @@
+version=$(.github/scripts/get-version.sh)
+if [[ $version =~ ^([0-9]+)\.([0-9]+)\.([0-9]+) ]]; then
+  major="${BASH_REMATCH[1]}"
+  minor="${BASH_REMATCH[2]}"
+  patch="${BASH_REMATCH[3]}"
+else
+  echo "unexpected version: $version"
+  exit 1
+fi
+if [[ $patch == 0 ]]; then
+  if [[ $minor == 0 ]]; then
+    prior_major=$((major - 1))
+    prior_minor=$(grep -Po "^## Version $prior_major.\K[0-9]+" CHANGELOG.md | head -1)
+    prior_version="$prior_major.$prior_minor"
+  else
+    prior_version="$major.$((minor - 1)).0"
+  fi
+else
+  prior_version="$major.$minor.$((patch - 1))"
+fi
+
+echo $prior_version

.github/workflows/generate-post-release-pr.yml

@@ -0,0 +1,61 @@
+name: Generate Post-Release PR
+on:
+  workflow_dispatch:
+
+jobs:
+  prereqs:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Verify prerequisites
+        run: |
+          if [[ $GITHUB_REF_NAME != main ]]; then
+            echo this workflow should only be run against main
+            exit 1
+          fi
+
+  create-pull-request-against-main:
+    runs-on: ubuntu-latest
+    needs:
+      - prereqs
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set environment variables
+        run: |
+          version=$(.github/scripts/get-version.sh)
+          if [[ $version =~ ^([0-9]+)\.([0-9]+)\.0$ ]]; then
+            major="${BASH_REMATCH[1]}"
+            minor="${BASH_REMATCH[2]}"
+            next_version="$major.$((minor + 1)).0"
+          else
+            echo "unexpected version: $version"
+            exit 1
+          fi
+          echo "NEXT_VERSION=$next_version" >> $GITHUB_ENV
+          echo "VERSION=$version" >> $GITHUB_ENV
+          prior_version=$(.github/scripts/get-prior-version.sh)
+          echo "PRIOR_VERSION=$prior_version" >> $GITHUB_ENV
+
+      - name: Use CLA approved github bot
+        run: .github/scripts/use-cla-approved-github-bot.sh
+
+      - name: Create pull request against main
+        env:
+          # not using secrets.GITHUB_TOKEN since pull requests from that token do not run workflows
+          GH_TOKEN: ${{ secrets.OPENTELEMETRYBOT_GITHUB_TOKEN }}
+        run: |
+          ./gradlew updateVersionInDocs -Prelease.version=$VERSION
+          ./gradlew japicmp -PapiBaseVersion=$PRIOR_VERSION -PapiNewVersion=$VERSION
+          ./gradlew --refresh-dependencies japicmp
+   
+          message="Post release for version $VERSION"
+          body="Post-release updates for version \`$VERSION\`."
+          branch="opentelemetrybot/post-release-for-${VERSION}"
+
+          git checkout -b $branch
+          git commit -a -m "$message"
+          git push --set-upstream origin $branch
+          gh pr create --title "$message" \
+                       --body "$body" \
+                       --base main