Upgrade npm to pnpm

[lakardion]

As much as a good default npm is, there are better tools out there that leverage caching solutions and make builds significantly faster.
Yarn was initially a good approach to this and pnpm followed.
Pnpm used to be an immature package manager but it has become very popular amongst library authors becoming a standard in modern js development.

https://pnpm.io/benchmarks

What this upgrade will bring to the table

• Faster CI/CD installs
• Faster local installs
• Readable yaml lock files (cut the package.lock / yarn.lock nonsense diffs)
  This might not be game changing bc who really reads lock files but if you ever want to check on sub deps of installed packages it is a nice to have!

[paribaker]

pnpm is not supported by heroku so we would have to have a different set up for heroku ? @lakardion

[whusterj]

@lakardion - This issue is getting stale, but I am interested in any strategy that will reduce build times. Can you revisit this and start a PR?