feat: add support for base64 images

[catalan-adobe]

Context

Contribution following code sample shared with customer to solve the issue on a specific project.

What it does

• Add support for Base64 images in preprocess function.
  Then, base64 images were removed
  Now, original base64 images are modified: the base64 inline data is replaced by an object URL (generated using https://developer.mozilla.org/en-US/docs/Web/API/URL/createObjectURL_static)
• Add Unit tests

How to test

1. Clone https://github.com/hlxsites/petplace
2. Checkout branch issue-28
3. From the root project, in a terminal, run hlx import to fetch latest helix-importer-ui then stop it already.
4. From tools/importer/helix-importer-ui/:
   • in package.json modify helix-importer dependency to adobe/helix-importer#feat-support-b64-images
   • rm node_modules
   • npm install
   • npm run build:dev
5. Re-start Helix Importer server without fetching helix-importer-ui project, hlx import --skip-ui
6. In Helix Importer UI:
   • use test URL https://www.petplace.com/article/breed/pembroke-welsh-corgi/
   • use importer script http://localhost:3001/tools/importer/import.js
   • run import
7. In Preview tab, confirm that you see following images in the "Care Tabs" block:
   

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.66%. Comparing base (b691d4a) to head (4fa0937).
Report is 40 commits behind head on main.

❗ Current head 4fa0937 differs from pull request most recent head cbc326d. Consider uploading reports for the commit cbc326d to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #154      +/-   ##
==========================================
- Coverage   97.66%   95.66%   -2.00%     
==========================================
  Files          21       14       -7     
  Lines        1800     1547     -253     
==========================================
- Hits         1758     1480     -278     
- Misses         42       67      +25     

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[catalan-adobe]

@kptdobe, should this implementation support svg+xml:base64 images? Shouldn't these be considered icons and thus, follow https://www.hlx.live/developer/block-collection/icons rather than being automatically imported as is?

[adobe-bot]

🎉 This PR is included in version 3.3.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀