add cache busting to assets in preview

[raclim]

Progress on #3156

Changes:

• Includes suggestion to implement cache busting by appending asset URLs with timestamps, which is happening in the function addCacheBustingtoAssets() in client/modules/Preview/previewIndex.jsx.

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123

[release-com]

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• p5.js-web-editor
  • app-ted814c.release.editor.p5js.org/
  • preview-ted814c.release.editor.p5js.org/

🔧Environment Status : https://app.release.com/public/Processing%20Foundation/env-4e97a99006