s3: report http.StatusOK if the directory is explicitly created

fix https://github.com/seaweedfs/seaweedfs/issues/3457

weed/server/filer_server_handlers_read.go

@@ -111,6 +111,10 @@ func (fs *FilerServer) GetOrHeadHandler(w http.ResponseWriter, r *http.Request)
 			w.WriteHeader(http.StatusMethodNotAllowed)
 			return
 		}
+		if entry.Attr.Mime != "" {
+			// inform S3 API this is a user created directory key object
+			w.Header().Set(s3_constants.X_SeaweedFS_Header_Directory_Key, "true")
+		}
 		fs.listDirectoryHandler(w, r)
 		return
 	}