add sparkjava application sample

Signed-off-by: Anca Iordache <anca.iordache@docker.com>

samples/sparkjava/sparkjava/src/main/java/App.java

@@ -0,0 +1,9 @@
+import static spark.Spark.*;
+
+public class App {
+    public static void main(String[] args) {
+        port(8080);
+
+        get("/", (req, res) -> "Hello world");
+    }
+}