Install new PnpM package manager

https://pnpm.io/

> Fast
> pnpm is up to 2x faster than npm
> 
> Efficient
> Files inside node_modules are cloned or hard linked from a single content-addressable storage
> 
> Supports monorepos
> pnpm has built-in support for multiple packages in a repository
> 
> Strict
> pnpm creates a non-flat node_modules by default, so code has no access to arbitrary packages