Add PyOperator

Signed-off-by: Kaiyuan Hu <kaiyuan.hu@zilliz.com>

select_video.py

@@ -16,10 +16,11 @@ from itertools import groupby
 from typing import List
 
 from towhee import register
+from towhee.operator import PyOperator
 
 
 @register(output_schema=['vec'])
-class SelectVideo:
+class SelectVideo(PyOperator):
     def __init__(self, top_k: int, reduce_function: str = 'sum', reverse: bool = True):
         self.top_k = top_k
         self.reduce_function = reduce_function