Merge pull request 'OZG-5058-mongock-setup' (#19) from OZG-5058-mongock-setup into master

pom.xml

...ain/java/de/ozgcloud/admin/AdministrationApplication.java

...ud/admin/migration/M001_CreateEmptyPostfachIfMissing.java

.../ozgcloud/admin/migration/MongockFailedEventListener.java

...e/ozgcloud/admin/migration/MongockStartEventListener.java

...ozgcloud/admin/migration/MongockSuccessEventListener.java

src/main/resources/application.yaml

...java/de/ozgcloud/admin/AdministrationApplicationTest.java

...in/migration/M001_CreateEmptyPostfachIfMissingITCase.java

src/test/resources/application-itcase.yaml