OZG-6477 OZG-6439 Implement CollaborationRemoteService.getById()

...a/de/ozgcloud/alfa/collaboration/CollaborationMapper.java

...gcloud/alfa/collaboration/CollaborationRemoteService.java

.../de/ozgcloud/alfa/collaboration/CollaborationService.java

...a/collaboration/CollaborationByVorgangControllerTest.java

.../ozgcloud/alfa/collaboration/CollaborationMapperTest.java

...ud/alfa/collaboration/CollaborationRemoteServiceTest.java

...ozgcloud/alfa/collaboration/CollaborationServiceTest.java

...lfa/collaboration/FachstelleCollaborationTestFactory.java

...fa/collaboration/GrpcFindRequestsResponseTestFactory.java

.../alfa/collaboration/GrpcGetRequestRequestTestFactory.java

...alfa/collaboration/GrpcGetRequestResponseTestFactory.java

...oration/OrganisationsEinheitCollaborationTestFactory.java