class_docstr: Combo Faiss Retrieval Flask resource.
  The PUT method is to get KNN tokens, add new chunks, reset index.
code: def reset(self):
      output = "success"
      if not self.updatable:
          return "no dynamic service, no action is performed"
      for i, service in enumerate(self.retrieval_services):
          if service.updatable:
              service.reset()
      return output
  
imports: import pickle
  import threading
  from typing import List, Union
  import faiss
  import numpy
  import torch
  from flask import Flask, jsonify, request
  from flask_restful import Api, Resource
  from nemo.collections.common.tokenizers.tokenizer_spec import TokenizerSpec
  from nemo.collections.nlp.modules.common.megatron.retrieval_services.retrieval_service import DynamicFaissRetrievalService, FaissRetrievalService
  from nemo.collections.nlp.modules.common.megatron.retrieval_services.util import lock
label_desc: Use image node_id 3 for calling the ComboRetrievalResource obj's underlying member method code with example usage: obj.reset() and returns: output, str