feat: lock pnpm version via npx

[rkristelijn]

• I've read and followed the contributing guide on how to create great pull requests.
• I've updated the relevant documentation for any new or updated feature.
• I've linked relevant GitHub issue with Closes request: use pnpm in dev dependency #4787
• I've added a visual demonstration in the form of a screenshot or video.

# get the version from package.json
❯ npm pkg get devDependencies.pnpm
"9.12.3"
# install a different version globally
❯ npm i pnpm@8 -g
# print the version of pnpm from within the repo root
❯ pnpm --version
# observe it can be different and therefore can cause issues
8.15.9
# whereas if you use npm pnpm, it always picks from the dev dependencies
❯ npx pnpm --version
9.12.3

[Janpot]

You can run pnpm through npx if you want but we won't recommend it. I think this PR can be closed.

[rkristelijn]

Can you elaborate a bit? I think my argument is valid, would like to understand your viewpoint

[Janpot]

pnpm is our package manager of choice, if you want to contribute we recommend installing it globally. If you don't want to do that, you can use something like corepack. Both of these methods will respect the packageManager field in our package.json and automatically use the configured version of pnpm. All maintainers of the mui ecosystem have a global pnpm, we don't need npx pnpm.

[rkristelijn]

@Janpot Thanks for the clarification, I would like to add this in the CONTRIBUTING.md, is that ok?

[rkristelijn]

https://github.com/mui/toolpad/pull/4793/files