build: Replace custom runVelocity task with run-velocity plugin, use run-waterfall in bungee example, update run-paper

also attach example build tasks to `assemble` instead of `build`

examples/example-jda/build.gradle.kts

@@ -15,7 +15,7 @@ dependencies {
 }
 
 tasks {
-    build {
+    assemble {
         dependsOn(shadowJar)
     }
 }