Use pnpm instead of npm (#1375)

Pnpm is like npm except instead of keeping multiple copies of
dependencies, it shares a single copy for multiple dependencies
significantly reducing build time and the space needed to hold all the
dependencies. Read [here](https://pnpm.io/motivation) for more info.

This changes our CI to use pnpm and allows developers to choose to use
pnpm instead of npm. Also, pnpm has a built-in node version manager so
devs no longer need to use nvm to work on photonvision. All npm
functionality (including photon-server gradle tasks) still functions
using npm so this isn't breaking. We should make a docs change to
suggest to use pnpm.

.github/workflows/photon-code-docs.yml

@@ -36,14 +36,20 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v4
+      - name: Install pnpm
+        uses: pnpm/action-setup@v4
+        with:
+          version: 9
       - name: Setup Node.js
         uses: actions/setup-node@v4
         with:
           node-version: 18
+          cache: 'pnpm'
+          cache-dependency-path: '**/pnpm-lock.yaml'
       - name: Install Dependencies
-        run: npm ci
+        run: pnpm install
       - name: Build Production Client
-        run: npm run build-demo
+        run: pnpm run build-demo
       - uses: actions/upload-artifact@v4
         with:
           name: built-client