Add a generic Walk()'er to list a bucket, optinally prefix (#9026)

This generic Walk() is used by likes of Lifecyle, or
KMS to rotate keys or any other functionality which
relies on this functionality.

cmd/storage-rest-server.go

@@ -431,10 +431,7 @@ func (s *storageRESTServer) WalkHandler(w http.ResponseWriter, r *http.Request)
 	}
 	leafFile := vars[storageRESTLeafFile]
 
-	endWalkCh := make(chan struct{})
-	defer close(endWalkCh)
-
-	fch, err := s.storage.Walk(volume, dirPath, markerPath, recursive, leafFile, readMetadata, endWalkCh)
+	fch, err := s.storage.Walk(volume, dirPath, markerPath, recursive, leafFile, readMetadata, r.Context().Done())
 	if err != nil {
 		s.writeErrorResponse(w, err)
 		return