Healthy Slow Cooker Chicken and Rice Soup

Name: Healthy Slow Cooker Chicken and Rice Soup
Ingredients: 5 stalks celery, sliced into 1/4-inch-thick chunks; 3 large carrots, sliced into 1/4-inch-thick chunks; 2 large sprigs dill, plus 1/4 cup chopped dill fronds and whole fronds, for serving; 2 large sprigs thyme; 1 bay leaf; 1/4 small onion, peeled and root end intact; Kosher salt and freshly ground black pepper; 2 pounds bone-in, skin-on chicken thighs (about 6 thighs); 8 cups low-sodium chicken broth; 2 cups cooked brown rice; 1 to 2 tablespoons freshly squeezed lemon juice