BAEL-1843 - JUnit4 -> JUnit5 migration guide (#4816)

* Added code for the migration from JUnit 4 to JUnit 5

* Add example for Rule migration support

* Add fix to access modifiers to test methods

* Remove wrong header

* Add junit5-migration module and its code snippets

* Add module configuration to pom

* Remove test classes that were added for the migration from JUnit 4 to JUnit 5 article (moved under correct module)

testing-modules/junit-5/src/test/java/com/baeldung/NestedUnitTest.java

@@ -10,13 +10,13 @@ import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 
 public class NestedUnitTest {
+
     Stack<Object> stack;
-    boolean isRun = false;
 
     @Test
     @DisplayName("is instantiated with new Stack()")
     void isInstantiatedWithNew() {
-        new Stack<Object>();
+        new Stack<>();
     }
 
     @Nested
@@ -25,7 +25,7 @@ public class NestedUnitTest {
 
         @BeforeEach
         void init() {
-            stack = new Stack<Object>();
+            stack = new Stack<>();
         }
 
         @Test