feat: Fix, refactor all openapi spec related configuration, add Visit api configuration

...ples/petclinic/rest/advice/ExceptionControllerAdvice.java

...amples/petclinic/rest/controller/OwnerRestController.java

.../samples/petclinic/rest/controller/PetRestController.java

...ples/petclinic/rest/controller/PetTypeRestController.java

...es/petclinic/rest/controller/SpecialtyRestController.java

...samples/petclinic/rest/controller/UserRestController.java

.../samples/petclinic/rest/controller/VetRestController.java

...amples/petclinic/rest/controller/VisitRestController.java

src/main/resources/openapi.yml

...s/petclinic/rest/controller/OwnerRestControllerTests.java

...les/petclinic/rest/controller/PetRestControllerTests.java

...s/petclinic/rest/controller/VisitRestControllerTests.java