[docs] Use codesandbox deploy for demos created from deploy previews

[eps1lon]

When creating a codesandbox from a demo in a netlify deploy preview i.e. deployed PRs we'll now use the packages built from the same PR. Before you would always create demos using the latest published version on NPM.

I could've used this a couple of times in the past when doing extensive manual testing i.e. manual e2e testing. Our capabilities are already limited for local testing but you could always work around it. It's more a convenience functionality when reviewing PRs.

Downside:

• deploy preview behaves different than actual published docs
• can be confusing when docs deploy finishes before codesandbox

Alternative:
Leave original functionality untouched but add an extra button in the "misc menu" for creating the demo using codesandbox deploys.

[mui-pr-bot]

Details of bundle changes

Generated by 🚫 dangerJS against 750d354

[oliviertassinari]

Nice! It's exactly what we discussed a few months ago with @mnajdova when she was working on the CSS utility classes and couldn't test it in code sandbox.

[eps1lon]

It's exactly what we discussed a few months ago with @mnajdova when she was working on the CSS utility classes and couldn't test it in code sandbox.

Right, I already forgot. Though you could always test it. You just had to know where to look for. Discoverability was almost non-existent. Hope this improves things. We'll need to make sure the deploy works. Booleans in environment variables are always a bit sketchy.