input: Write a python function to create a Flask route that returns a JSON response with a custom message.
  assert get_json_message() == {'message': 'Hello, this is a custom JSON response!'}
  assert get_json_message('Welcome to the API!') == {'message': 'Welcome to the API!'}
  assert get_json_message('Test message') == {'message': 'Test message'}
output: from flask import Flask, jsonify, request
  
  app = Flask(__name__)
  
  @app.route('/json-message')
  def get_json_message():
      message = request.args.get('message', 'Hello, this is a custom JSON response!')
      return jsonify({'message': message})
  
  if __name__ == '__main__':
      app.run(debug=True)