add assertion

Author: ywangd

server/src/main/java/org/elasticsearch/repositories/RepositoriesService.java

@@ -912,6 +912,8 @@ public Repository createRepository(ProjectId projectId, RepositoryMetadata repos
      * repository is at the cluster level.
      */
     public Repository createNonProjectRepository(RepositoryMetadata repositoryMetadata) {
+        assert DiscoveryNode.isStateless(clusterService.getSettings())
+            : "outside stateless only project level repositories are allowed: " + repositoryMetadata;
         return createRepository(null, repositoryMetadata, typesRegistry, RepositoriesService::throwRepositoryTypeDoesNotExists);
     }