Add support to use a particular branch of the SDK for QA testing purposes

[cazala]

🎉 Description

Add a query param to load the SDK from a specific branch/PR so QA can test the branch in the context of the Builder, which allows them to test more use cases and catch integration issues earlier.

• 🐛 This is a bug report.
• 📈 This is a feature request.

📝 Details

The @dcl/inspector is a static webapp served from the Builder's own assets, but when a PR is created in the SDK repo, a preview is always deployed to cloudflare pages. So technically we could pass a query param, like ?sdk-branch=fix/something telling the Builder to load the assets of the editor from a particular PR, get the CF pages url, and use that instead of the local url.