task: Add Composite Entity pattern (#1705)

* add composite entity pattern

* add composite entity pattern

* Update ReactorTest.java

* resolve some code quality problems

* modified a lot

* remove some extra codes

* modified README

* removed the author name and adjusted the spacing

Co-authored-by: zwebrain <11811721@mail.sustech.edu.cn>
Co-authored-by: Subhrodip Mohanta <hello@subho.xyz>

composite-entity/src/main/java/com/iluwatar/compositeentity/MessageDependentObject.java

@@ -0,0 +1,9 @@
+package com.iluwatar.compositeentity;
+
+/**
+ * The first DependentObject to show message.
+ */
+
+public class MessageDependentObject extends DependentObject<String> {
+
+}