(auto)configuration of file manager and dummy implementation as fallback

.../ozgcloud/apilib/file/dummy/DummyOzgCloudFileService.java

...de/ozgcloud/apilib/file/grpc/GrpcOzgCloudFileService.java

...java/de/ozgcloud/apilib/file/grpc/OzgCloudFileMapper.java

...de/ozgcloud/apilib/vorgang/dummy/DummyVorgangService.java

...emo/src/main/java/de/ozgcloud/apilib/demo/DemoRunner.java

api-lib-demo/src/main/resources/application.yml

...client/autoconfigure/OzgCloudClientAutoConfiguration.java

...d/client/autoconfigure/OzgCloudFileManagerProperties.java

...lient/autoconfigure/OzgCloudVorgangManagerProperties.java