input: Write a function to design a web server in Python using the Flask framework that serves a JSON object containing the current temperature for a city based on the city name given in the request. The function should return the Flask application object.
  assert design_temperature_server('New York') == "<Flask 'app'>"
  assert design_temperature_server('London') == "<Flask 'app'>"
  assert design_temperature_server('Tokyo') == "<Flask 'app'>"
  assert design_temperature_server('Sydney') == "<Flask 'app'>"
  assert design_temperature_server('Berlin') == "<Flask 'app'>"
output: from flask import Flask, jsonify
  
  def design_temperature_server(city):
      app = Flask(__name__)
      
      @app.route('/temperature/<city_name>', methods=['GET'])
      def get_temperature(city_name):
          # Dummy temperature data for demonstration
          temperatures = {
              'New York': 15,
              'London': 10,
              'Tokyo': 20,
              'Sydney': 25,
              'Berlin': 12
          }
          temperature = temperatures.get(city_name, 'City not found')
          return jsonify({'city': city_name, 'temperature': temperature})
      
      return app