input: Write a function to create a Python Flask app that listens for POST requests on the '/webhook' route. Upon receiving a request, the function should extract necessary parameters from the request and call the 'makeWebhookResult' function to generate a JSON response. The JSON response should contain 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()==True
  assert create_flask_app()==True
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 True
  