Migrate tests to AssertJ

Refactor all existing tests to use AssertJ assertions.

initializr-service/src/test/java/io/spring/initializr/service/extension/ReactorTestRequestPostProcessorTests.java

@@ -56,4 +56,4 @@ public class ReactorTestRequestPostProcessorTests
 				.hasSpringBootStarterTest().hasDependenciesCount(2);
 	}
 
-}
+}

initializr-service/src/test/java/io/spring/initializr/service/info/CloudFoundryInfoContributorTests.java

@@ -58,4 +58,4 @@ public class CloudFoundryInfoContributorTests {
 		return builder.build();
 	}
 
-}
+}