Remove the bag of gizzards and discard (or reserve for stock). Pat the chicken dry with paper towels.
Mix all the seasoning ingredients together in a bowl. Rub the entire chicken with seasonings, including under the skin. Transfer the chicken to the slow cooker, breast-side up.
Squeeze and reserve the juice from one of the lemons. Stuff the rinds into the cavity of the chicken along with one whole bouillon cube and a few garlic cloves. Crumble the other bouillon cube over the chicken and rub it into the skin.
Arrange the remaining lemon quarters, the rest of garlic cloves, and the thyme around the chicken.
Combine the reserved lemon juice, the soy sauce, and the broth, and pour it over the chicken.
Place the lid on the slow cooker and cook on high heat for 4 to 5 hours. Thirty minutes or so before the time is done, add the rosemary sprigs.
Remove chicken from the slow-cooker and allow it to rest on a baking sheet, tented with foil, for about 20 minutes. The wings and drumsticks may fall away as you lift the chicken; this is normal.Gravy
While the chicken is resting, strain the cooking liquid into a sauce pan and bring to a rapid simmer.
Scoop out a half cup of the liquid and whisk it with the flour in a separate bowl. Slowly pour the flour slurry back into the cooking liquid while whisking. Continue simmering and whisking until the gravy thickens. Taste and add salt and pepper as desired.
Serve the chicken with gravy and whatever sides you choose.