Use Node-standard corepack to install pnpm

[rmunn]

Will fix #75.

[rmunn]

Note that I'm not certain if corepack enable is the right command for dev machines. I think it is, since it certainly is the right command for the Dockerfile. But since I have pnpm already installed, I can't tell for certain that corepack enable is pulling in pnpm. Someone who does not have pnpm installed globally will need to test this and then verify that that's the right command as opposed to corepack prepare pnpm@latest --activate.

[hahn-kev]

It looks good to me, I've already enabled corepack and installed pnpm with it, but running corepack enable now doesn't break anything, so I'm fine to merge it in and see what issues we run into.