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>

pom.xml

@@ -224,6 +224,7 @@
         <module>parameter-object</module>
         <module>active-object</module>
         <module>model-view-viewmodel</module>
+        <module>composite-entity</module>
     </modules>
 
     <repositories>