feat: create builder to factory method

Signed-off-by: Otavio Santana <[email protected]>

Author: otaviojava

src/main/java/com/otaviojava/demos/ddd/Product.java

@@ -88,4 +88,8 @@ public String toString() {
                 ", categories=" + categories +
                 '}';
     }
+
+    public static ProductBuilder builder() {
+        return new ProductBuilder();
+    }
 }