Hot Dogs and Bratwurst with Sauerkraut and Relish

Name: Hot Dogs and Bratwurst with Sauerkraut and Relish
Ingredients: 1 tbsp. olive oil; 1 small onion, thinly sliced; 1/2 tsp. caraway seeds; 1/2 tsp. mustard seeds; 1 1-pound bag sauerkraut, drained and rinsed; 3 tbsp. apple cider vinegar; 1 c. sweet pickle relish; 1 small stalk celery, finely chopped; 1 scallion, finely chopped; 1 tbsp. finely chopped pickled jalapeños; Vegetable oil, for the grill; 8 links fresh bratwurst; 8 hot dogs; 4 tbsp. salted butter, softened; 16 split-top hot dog buns; Yellow mustard, for serving