Replace yarn with another package manager

[mimarz]

We've had enough small weird issues with using yarn locally and on gh actions.

These include:

• Hoisting of dependencies has caused unwanted bugs downstream
• yarn pack differs from npm pack with ignoring some files
• yarn add vercel suddenly stopped working on gh actions

Feels like its time to move on to a more modern package manager.

pnpm is at the top of the list as an replacement, but we are free to explore other posibilites, Deno 2.0 looks interesting?

Things to look out for when changing package manager

• We use yarn foreach for building packages based on dependencies between them.
• Has to work with Renovate