input: def webhook_response_generator(request_json):
      """
      Generates a JSON response for a POST request sent to the '/webhook' route in a Flask app.
      The function extracts necessary parameters from the request and calls 'makeWebhookResult' to generate the response.
      The response contains a 'speech' field with text to be spoken by a voice assistant.
      
      >>> webhook_response_generator('{ "result": { "action": "productos.sura", "parameters": { "tipo_cliente": "particular" } } }')
      {'speech': 'Buscando productos para particular', 'displayText': 'Buscando productos para particular', 'source': 'apiai-onlinestore-shipping'}
      >>> webhook_response_generator('{ "result": { "action": "producto.info", "parameters": { "producto": "hogar" } } }')
      {'speech': '<div class="textRightColumn">...</div>', 'displayText': '<div class="textRightColumn">...</div>', 'source': 'apiai-onlinestore-shipping'}
      """
      import json
  
      req = json.loads(request_json)
      res = makeWebhookResult(req)
      return res
output:     import json
  
      req = json.loads(request_json)
      res = makeWebhookResult(req)
      return res