Support pnpm; add Next.js

[GeoffreyBooth]

I’d like to add Next.js to CITGM. It uses pnpm to install dependencies, and before its tests can run it needs to be built. See https://github.com/vercel/next.js/blob/canary/contributing/core/developing.md.

Can we add support for pnpm like we do for yarn? And also another flag like build: true that when set runs <npm/yarn/pnpm> run build before running <npn/yarn/pnpm> test?

cc @Ethan-Arrowood

[targos]

pnpm: sure if someone contributes it
Build script: already possible. You can provide an array of scripts to run.

[Ethan-Arrowood]

FYI I've made relative teams aware of this internally at Vercel. I'll do my best to facilitate someone to assist with adding Next.js once pnpm is supported.

[Ethan-Arrowood]

For cross reference, adding Next.js to CITGM will help deter events such as: nodejs/node#50269

[styfle]

I created a PR here: #1044