input: Write a python function to fetch weather data for a given date and region using the OpenWeatherMap API.
  assert fetch_weather_data('London', '2023-10-01')['city']['name'] == 'London'
  assert fetch_weather_data('New York', '2023-10-02')['city']['name'] == 'New York'
  assert fetch_weather_data('Tokyo', '2023-10-03')['city']['name'] == 'Tokyo'
output: import requests
  
  def fetch_weather_data(city, date):
      api_key = 'YOUR_API_KEY'  # Replace with your OpenWeatherMap API key
      url = f'http://api.openweathermap.org/data/2.5/forecast?q={city}&appid={api_key}&units=metric'
      response = requests.get(url)
      data = response.json()
  
      # Find the closest forecast to the given date
      for entry in data['list']:
          if date in entry['dt_txt']:
              return {'city': data['city'], 'weather': entry}
  
      return None