OZG-6748 KOP-2733 XtaClientITCase: Test fetchMessages

src/main/java/de/ozgcloud/xta/client/XtaClient.java

src/main/java/de/ozgcloud/xta/client/XtaClientFactory.java

...n/java/de/ozgcloud/xta/client/config/XtaClientConfig.java

src/main/java/de/ozgcloud/xta/client/model/XtaFile.java

...est/java/de/ozgcloud/xta/client/XtaClientFactoryTest.java

src/test/java/de/ozgcloud/xta/client/XtaClientITCase.java

...de/ozgcloud/xta/client/config/XtaConfigValidatorTest.java

...zgcloud/xta/client/extension/XtaMessageExampleLoader.java

...xta/client/extension/XtaServerSetupExtensionTestUtil.java

...oud/xta/client/extension/XtaTestServerSetupExtension.java