input: def get_current_datetime_web_api():
      """
      Creates a simple web API using Flask that returns the current date and time when accessed.
      
      Example:
      Accessing the route '/datetime' should return the current date and time in the format "YYYY-MM-DD HH:MM:SS".
      Example output when accessed at '2023-10-05 14:30:45':
      "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_datetime():
          current_time = datetime.now().strftime("%Y-%m-%d %H:%M:%S")
          return jsonify(current_time)
  
      if __name__ == '__main__':
          app.run(debug=True)
  