input: def current_datetime_API() -> None:
      """Create a web API using Flask to provide the current date and time.
      The API should respond with the current date and time formatted as "YYYY-MM-DD HH:MM:SS".
      Example:
      When the API is accessed at the '/datetime' endpoint, it should return something like:
      "2023-10-05 14:30:45"
      """
  
output:     
      from flask import Flask, jsonify
      from datetime import datetime
  
      app = Flask(__name__)
  
      @app.route('/datetime', methods=['GET'])
      def get_current_datetime():
          now = datetime.now()
          formatted_datetime = now.strftime("%Y-%m-%d %H:%M:%S")
          return jsonify({"current_datetime": formatted_datetime})
  
      if __name__ == '__main__':
          app.run(debug=True)
  