[Internal] Support building with pnpm

[Spaceface16518]

Overview

Currently, building hackportal requires you to use npm. As alternative build tools like pnpm become more popular, it would be helpful to provide support for them out of the box. This will enable faster installs, faster builds, and lower disk storage sizes on developer computers. npm will still be used for deployment, but support for pnpm will be a great developer convenience due to several of pnpm's features.

Proposal

This wouldn't be a difficult change. I use pnpm to develop hackportal. Supporting pnpm out of the box mostly amounts to explicitly specifying peer dependencies that npm installs automatically. The reason this is an issue at all is explained in pnpm's pnpm vs npm docs page.