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/test/java/com/iluwatar/compositeentity/AppTest.java

@@ -0,0 +1,25 @@
+package com.iluwatar.compositeentity;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * com.iluwatar.compositeentity.App running test
+ */
+class AppTest {
+
+  /**
+   * Issue: Add at least one assertion to this test case.
+   * <p>
+   * Solution: Inserted assertion to check whether the execution of the main method in {@link
+   * App#main(String[])} throws an exception.
+   */
+
+  @Test
+  void shouldExecuteApplicationWithoutException() {
+
+    assertDoesNotThrow(() -> App.main(new String[]{}));
+
+  }
+}