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

## 🎉 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.
* [x] 📈 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.