Slow Cooker Whole Chicken Soup

Name: Slow Cooker Whole Chicken Soup
Ingredients: 1 tablespoon olive oil; 1 medium yellow onion, diced; 4 medium carrots; 3 medium celery stalks; 8 cups (2 quarts) water; 1/2 teaspoon dried thyme; 2 bay leaves; 1 (4- to 5-pound) whole chicken, neck and giblets removed from the cavity; 1 tablespoon kosher salt, plus more as needed; 1/2 teaspoon freshly ground black pepper, plus more as needed; 2 tablespoons coarsely chopped fresh Italian parsley leaves; 2 cups cooked rice or noodles (optional)