[Backport 14.6] Support setting a label for a version (history) of a document

See https://docs.google.com/document/d/1BGThfhu-X2Ls_GaPr9CcRPOY2jxMybfN8YZyU373uv8

We need workflow support to set label info, something like:

@WorkflowAction(LABEL_VERSION)
Document labelVersion(String frozenNodeId, String label)
throws WorkflowException, RepositoryException, RemoteException;

@WorkflowAction(LABEL_VERSION)
Document removeLabelVersion(String frozenNodeId)
throws WorkflowException, RepositoryException, RemoteException;