Cajun Macaroni Salad

Name: Cajun Macaroni Salad
Ingredients: 1 small red onion, finely chopped; Kosher salt; 8 ounces elbow macaroni; 1/4 cup milk; 1/2 cup mayonnaise; 1/4 cup sour cream; 2 tablespoons Creole mustard; 1/2 cup chopped pickled okra or pickled green beans, plus 1/4 cup brine; 1 teaspoon sugar; 1 to 2 teaspoons hot sauce; 2 bell peppers (1 red, 1 yellow), chopped; 2 stalks celery, chopped, plus 1/2 cup chopped leaves; 1/4 cup chopped fresh parsley