[savedObjectClient] decorate non-es errors too (#13596)

(cherry picked from commit 8141e3f)

src/server/saved_objects/client/saved_objects_client.js

@@ -142,7 +142,7 @@ export class SavedObjectsClient {
     });
 
     if (response.found === false) {
-      throw Boom.notFound();
+      throw errors.decorateNotFoundError(Boom.notFound());
     }
   }