Slow Cooker Chicken and Dumplings

Name: Slow Cooker Chicken and Dumplings
Ingredients: 2 pounds bone-in chicken thighs (skin-on or skinless, your choice); 2 medium carrots (peeled and sliced); 2 stalks celery (diced); 1 large onion (diced); 3 cloves garlic (minced); 4 cups chicken broth; 2 teaspoons dried thyme; 1 teaspoon dried rosemary; 1 teaspoon salt (to taste); 1/2 teaspoon black pepper (freshly ground); 1 cup flour (for dumplings); 2 teaspoons baking powder (for dumplings); 1/2 cup milk (for dumplings); 2 tablespoons butter (for dumplings)