input: Write a function to create a Python Flask app that listens for POST requests on the '/webhook' route. When a request is received, extract the necessary parameters from the request and call the 'makeWebhookResult' function to generate a response. The response should be a JSON object containing a 'speech' field with the text to be spoken by the voice assistant. The app should be started on port 5000 and run in debug mode.
  
  assert create_flask_app() == "Starting app on port 5000"
  assert makeWebhookResult({"result": {"action": "productos.sura", "parameters": {"tipo_cliente": "corporativo"}}) == {'speech': 'Buscando productos para corporativo', 'displayText': 'Buscando productos para corporativo', 'source': 'apiai-onlinestore-shipping'}
output: from flask import Flask, request, jsonify
  
  def create_flask_app():
      app = Flask(__name__)
  
      @app.route('/webhook', methods=['POST'])
      def webhook():
          req = request.get_json(silent=True, force=True)
          res = makeWebhookResult(req)
          return jsonify(res)
  
      app.run(port=5000, debug=True)
      return "Starting app on port 5000"