build(hw-02): replace Gradle project with Maven setup

* remove Gradle wrapper and project configuration
* remove default Gradle application and test sources
* add Maven pom.xml
* add Maven configuration files

second-part/hw-02/user-service/src/main/java/com/example/App.java

@@ -0,0 +1,10 @@
+package com.example;
+
+/**
+ * Hello world!
+ */
+public class App {
+    public static void main(String[] args) {
+        System.out.println("Hello World!");
+    }
+}