[✨] Stackblitz pkg.pr.new templates

[maiieul]

Would be cool to have the pkg.pr.new templates work. This would allow people to play with the components live. But maybe there are better/simpler approaches for us.

It's not easy with nx because stackblitz expects a standalone repository (think something like the output of pnpm create qwik@latest).

maiieul: I made an attempt in #863, but I had to create a standalone repository without nx inside our nx monorepo, and install @qwik-ui/headless in the root package.json, which we're not supposed to do with nx.

We also need to think if we really want to maintain a "sink".

Potential solutions:

1. install nx inside the standalone repository as well
2. write a script executed on CI that copies the component files and puts them into a standalone fresh pnpm create qwik@latest project so that it easily works out of the box in stackblitz