`pnpm` is our package manager of choice. This repository contains
framework starter templates, which check-in lockfiles to speed up clone
& deploy time. This PR updates a few frameworks to use `pnpm` instead of
`yarn` or `npm`.
- Updates Gatsby to Gatsby 5 given Node.js 18 support
- Updates to latest Nuxt 3 template for stable version
- Updates Astro to latest stable version, previously on RC
- Updates Angular to v15, previously on v13
