new (message) properties for the error and code fields of the exceptions

annotation-web/src/main/resources/messages_en.properties

@@ -18,7 +18,10 @@ error.annotation_not_found=No annotation found with the given identifier! {0}
 error.annotation_apikey_file_not_found=No apiKey file found in {0} folder!
 #error.annotation_operation_not_authorized=The user is not allowed to perform the given operation!
 error.annotation_client_not_authorized=The client application is not allowed to perform the given operation!
-error.annotation_client_not_public=The client is not authorized to perform the given operation because the public id for the client is missing. Please get in contact with the Europeana APIs customer support via [email protected]
+
+error.annotation_client_not_public=The client is not authorised to perform the given operation because the public id for the client is missing. Please get in contact with the Europeana APIs customer support via [email protected]
+error.annotation_client_not_public.label=Client not authorised due to missing public id
+error.annotation_client_not_public.code=403_client_not_public
 
 error.annotation_invalid_token=The provided authentication token is invalid! {0}
 error.annotation_user_not_authorized=The user is not authorized to perform the given action! {0}