fix(java): surpress maven output in cdk.json (#3624)

Update the java app init template to use use `--quiet` when running `mvn exec`
so that output can be parsed.

Fixes #3571

packages/aws-cdk/lib/init-templates/app/java/cdk.json

@@ -1,3 +1,3 @@
 {
-  "app": "mvn exec:java"
+  "app": "mvn -q exec:java"
 }