Migrate to pnpm

[hleepfl]

Switching over from npm to pnpm. Reasons are : it's faster, uses less disk space, forces stricter definition of dependencies and makes monorepo management easier (catalog feature for example)
Again I recommend reviewing by commit

Notes

• I had to pin exact dependency versions. pnpm doesn't like major version only, and some minor version changes were breaking things anyways
• Shared dependencies which need to be the same version can be defined in catalog
• I had to remove the polyfill lib in webapp and polyfill Buffer by hand instead. The library had bugs that hadn't been fixed since like 8 minor versions.

Also I haven't been able to test npm publishing yet. I'm like 50% confident