Enhance Github release notes (aws-observability#487)

*Issue #, if available:*

*Description of changes:*
DO NOT MERGE until
aws-observability#461
has been merged.

Add CHANGELOG entries to Github release notes and use headers to
separate new changes, upstream components, release artifacts, and Lambda
layer ARNs.

Tested in my own repo:
https://github.com/ezhang6811/release-workflow-test/actions/runs/18236310430/job/51930597871

Mock release created:
https://github.com/ezhang6811/release-workflow-test/releases/tag/v2.0.1

By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice.

---------

Co-authored-by: Thomas Pierce <[email protected]>

Author: ezhang6811

.github/workflows/release-build.yml

@@ -81,8 +81,10 @@ jobs:
     steps:
       - name: Set up regions matrix
         id: set-matrix
+        env:
+          AWS_REGIONS: ${{ github.event.inputs.aws_region }}
         run: |
-          IFS=',' read -ra REGIONS <<< "${{ github.event.inputs.aws_region }}"
+          IFS=',' read -ra REGIONS <<< "$AWS_REGIONS"
           MATRIX="["
           for region in "${REGIONS[@]}"; do
             trimmed_region=$(echo "$region" | xargs)
@@ -375,39 +377,60 @@ jobs:
         id: create_release
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          VERSION: ${{ github.event.inputs.version }}
         run: |
           # Extract all dependencies from pyproject.toml
           DEPS=$(python3 -c "
-            import re
-            with open('aws-opentelemetry-distro/pyproject.toml', 'r') as f:
-                content = f.read()
-            deps_match = re.search(r'dependencies\s*=\s*\[(.*?)\]', content, re.DOTALL)
-            if deps_match:
-                deps_content = deps_match.group(1)
-                dep_lines = re.findall(r'\"([^\"]+)\"', deps_content)
-                formatted_deps = []
-                for dep_line in dep_lines:
-                    if ' == ' in dep_line:
-                        package, version = dep_line.split(' == ', 1)
-                        formatted_deps.append(f'- \`{package}\` - {version}')
-                    else:
-                        formatted_deps.append(f'- \`{dep_line}\`')
-                print('\n'.join(formatted_deps))
+          import re
+          with open('aws-opentelemetry-distro/pyproject.toml', 'r') as f:
+              content = f.read()
+          deps_match = re.search(r'dependencies\s*=\s*\[(.*?)\]', content, re.DOTALL)
+          if deps_match:
+              deps_content = deps_match.group(1)
+              dep_lines = re.findall(r'\"([^\"]+)\"', deps_content)
+              formatted_deps = []
+              for dep_line in dep_lines:
+                  if ' == ' in dep_line:
+                      package, version = dep_line.split(' == ', 1)
+                      formatted_deps.append(f'- \`{package}\` - {version}')
+                  else:
+                      formatted_deps.append(f'- \`{dep_line}\`')
+              print('\n'.join(formatted_deps))
+          ")
+
+          # Extract CHANGELOG entries for this version
+          CHANGELOG_ENTRIES=$(python3 -c "
+          import re, os
+          version = os.environ['VERSION']
+          with open('CHANGELOG.md', 'r') as f:
+              content = f.read()
+          version_pattern = rf'## v{re.escape(version)}.*?\n(.*?)(?=\n## |\Z)'
+          version_match = re.search(version_pattern, content, re.DOTALL)
+          if version_match:
+              entries = version_match.group(1).strip()
+              if entries:
+                  print(entries)
           ")
 
           # Create release notes
           cat > release_notes.md << EOF
-          This release contains the following upstream components:
+          $(if [ -n "$CHANGELOG_ENTRIES" ]; then echo "## What's Changed"; echo "$CHANGELOG_ENTRIES"; echo ""; fi)
+
+          ## Upstream Components
 
           $DEPS
 
-          This release also publishes to public ECR and PyPi.
-          * See ADOT Python auto-instrumentation Docker image v${{ github.event.inputs.version }} in our public ECR repository:
+          ## Release Artifacts
+
+          This release publishes to public ECR and PyPi.
+          * See ADOT Python auto-instrumentation Docker image v$VERSION in our public ECR repository:
           https://gallery.ecr.aws/aws-observability/adot-autoinstrumentation-python
-          * See version ${{ github.event.inputs.version }} in our PyPi repository:
+          * See version $VERSION in our PyPi repository:
           https://pypi.org/project/aws-opentelemetry-distro/
 
-          This release also includes the AWS OpenTelemetry Lambda Layer for Python version ${{ github.event.inputs.version }}-$(echo $GITHUB_SHA | cut -c1-7).
+          ## Lambda Layer
+
+          This release includes the AWS OpenTelemetry Lambda Layer for Python version $VERSION-$(echo $GITHUB_SHA | cut -c1-7).
 
           Lambda Layer ARNs:
           ${{ needs.generate-lambda-release-note.outputs.layer-note }}
@@ -417,10 +440,10 @@ jobs:
           shasum -a 256 layer.zip > layer.zip.sha256
 
           gh release create --target "$GITHUB_REF_NAME" \
-             --title "Release v${{ github.event.inputs.version }}" \
+             --title "Release v$VERSION" \
              --notes-file release_notes.md \
              --draft \
-             "v${{ github.event.inputs.version }}" \
+             "v$VERSION" \
              ${{ env.ARTIFACT_NAME }} \
              ${{ env.ARTIFACT_NAME }}.sha256 \
              layer.zip \