input: Write a function to create a web API using Python and Flask that returns the current date and time. The function should define a route `/datetime` and return the current date and time formatted as "YYYY-MM-DD HH:MM:SS".
  
  
  def create_datetime_api():
      from flask import Flask
      import datetime
  
      app = Flask(__name__)
  
      @app.route('/datetime')
      def get_datetime():
          return datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")
  
      if __name__ == '__main__':
          app.run()
  
output: def create_datetime_api():
      from flask import Flask
      import datetime
  
      app = Flask(__name__)
  
      @app.route('/datetime')
      def get_datetime():
          return datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")
  
      if __name__ == '__main__':
          app.run()