Save files in local storage as group readable

Go creates temporary files as 600 (https://github.com/golang/go/blob/334a591a3f4d868368913328b3e81ddf5b0f46fa/src/os/tempfile.go#L44), but sometimes we want the group to be able to read them (for example, for another user to back up the storage.)

modules/storage/local.go

@@ -102,6 +102,9 @@ func (l *LocalStorage) Save(path string, r io.Reader, size int64) (int64, error)
 	if err := util.Rename(tmp.Name(), p); err != nil {
 		return 0, err
 	}
+	if err := os.Chmod(p, 0o640); err != nil {
+		return 0, err
+	}
 
 	tmpRemoved = true