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.

photon-server/build.gradle

@@ -1,7 +1,7 @@
 plugins {
     id "application"
     id 'com.github.johnrengelman.shadow' version '8.1.1'
-    id "com.github.node-gradle.node" version "7.0.1"
+    id "com.github.node-gradle.node" version "7.0.2"
     id "org.hidetake.ssh" version "2.11.2"
     id 'edu.wpi.first.WpilibTools' version '1.3.0'
 }
@@ -32,17 +32,23 @@ shadowJar {
 }
 
 node {
+    download = true
+    version = "18.20.4"
     nodeProjectDir = file("${projectDir}/../photon-client")
 }
 
-tasks.register('copyClientUIToResources', Copy) {
+tasks.register('buildUI', PnpmTask) {
+    args = ["run", "build"]
+}
+
+tasks.register('copyUIToResources', Copy) {
     from "${projectDir}/../photon-client/dist/"
     into "${projectDir}/src/main/resources/web/"
 }
 
 tasks.register("buildAndCopyUI") {
-    dependsOn "npm_run_build"
-    finalizedBy "copyClientUIToResources"
+    dependsOn "buildUI"
+    finalizedBy "copyUIToResources"
 }
 
 run {