Implement conflict handling for NIB entities

api/go/gosdn/conflict/conflict.pb.go

api/go/gosdn/rbac/user.pb.go

api/go/gosdn/topology/node.pb.go

api/openapiv2/gosdn_northbound.swagger.json

api/proto/gosdn/conflict/conflict.proto

api/proto/gosdn/rbac/user.proto

api/proto/gosdn/topology/node.proto

cli/cmd/userUpdate.go

controller/api/apiUtil_test.go

controller/api/user_test.go

controller/conflict/versioning.go

controller/controller.go

controller/interfaces/rbac/rbacService.go

controller/interfaces/rbac/user.go

controller/northbound/server/test_util_test.go

controller/northbound/server/user.go

controller/northbound/server/user_test.go

controller/rbac/databaseUserStore.go

controller/rbac/rbacService.go

controller/rbac/user.go