fix: DA upload should rewrite asset references to PNG when images-to-png is enabled

[hmehta-adobe]

Summary

When running aem-import-helper da upload with the default --images-to-png flag (true), WEBP assets are downloaded and converted to PNG before upload, but the HTML references still point to their original .webp filenames.

Expected

• Assets are converted to PNG (already happens).
• Updated HTML references should point to the .png filenames so DA serves the converted files.

Steps to reproduce

1. Run aem-import-helper da upload against a page containing .webp images.
2. Inspect the console output: upload logs show .png files, but the “Updating asset references” log still rewrites to .webp.
3. Deployed HTML points to .webp URLs that fail in DA.