add errors, warnings, infos to RetrieveResponse

proto/caosdb/entity/v1alpha1/main.proto

@@ -125,6 +125,12 @@ message ByIdRequest {
 message RetrieveResponse {
   // Payload of the retrieval
   Entity entity = 1;
+  // Transaction errors.
+  repeated Message errors = 2;
+  // Transaction warnings.
+  repeated Message warnings = 3;
+  // Transaction info messages.
+  repeated Message infos = 4;
 }
 
 // Wrapper for different kinds of retrievals (currently, only by ID). We need