Fix changelog title inference

[cotti]

This pull request enhances the changelog GitHub Actions by ensuring the PR body and body change status are consistently captured and passed through the workflow, similar to how the PR title is handled. This improves the accuracy and flexibility of changelog automation, especially for workflows that depend on PR body content or need to detect changes to it.

Changelog Action Enhancements:

• The PR body (PR_BODY) is now captured and passed as an output in both the fetch-pr-data.js script and the changelog/submit/action.yml workflow, ensuring downstream steps have access to the PR body. [1] [2]
• The PR body is also made available in the changelog/validate/action.yml workflow, aligning it with how the PR title is handled.

Change Detection Improvements:

• A new output (BODY_CHANGED) is added to detect if the PR body has changed, similar to the existing title change detection. This is then used to conditionally set a --body-changed flag in the validation script. [1] [2]

Changelog Metadata Passing:

• The changelog submission workflow now passes the changelog description (CHANGELOG_DESCRIPTION) to downstream steps, ensuring all relevant metadata is available for changelog generation.