Resolve: #154 - Update RetrieveJob to support completion report

common/dataStructures/RetrieveRequest.hpp

frontend-grpc/FrontendGRpcSvc.cpp

frontend/common/WorkflowEvent.cpp

objectstore/RetrieveQueueAlgorithms.hpp

objectstore/RetrieveRequest.cpp

objectstore/RetrieveRequest.hpp

objectstore/cta.proto

scheduler/OStoreDB/OStoreDB.cpp

scheduler/OStoreDB/OStoreDB.hpp

scheduler/RetrieveJob.cpp

scheduler/RetrieveJob.hpp

scheduler/Scheduler.cpp

scheduler/SchedulerDatabase.hpp

scheduler/SchedulerTest.cpp