Migrate to pnpm

[frandiox]

PNPM is a faster and more modern alternative to Yarn v1. Most of the Vite ecosystem is using it, including Vite itself. Also, Vite CI has problems running Hydrogen with Yarn v1.

We already tried this back in Oct 2021, and we had issues with symlinks in pnpm.

Things to check:

• Compatibility with pnpm symlinks
• Peer depedencies support (do we need --shamefully-hoist?)
• Make sure standalone apps work the same way as in-repo examples

[michenly]

• Check to ensure PNPM works with shipit

[frehner]

Currently having issues with upgrading eslint in our repos, and the culprit appears to be yarn v1... 🤔

[benjaminsehl]

I'd love to have pnpm support!

[tylerhellner]

The monorepo of our organization runs on pnpm. I'd love to see support in the future so I can take it out of submodule status. If the team needs a hand with the PR, I'd be happy to look into it.

[frandiox]

@tylerhellner We are not currently working on this yet so feel free to take a stab at it 👍
The main priority is that our local development in the repo templates/examples should behave the same way as running standalone apps. This might be affected by differences in symlinks, etc.