Preheat the oven to 400°F. Place the chicken wings on a baking sheet; drizzle with the oil. Toss to coat. Bake at 400°F until crispy and well browned, but not charred, 25 minutes. Place the chicken wings, 7 cups water, onion, peppercorns, parsley, and garlic in a large saucepan over medium-high. Bring to a boil. Reduce the heat to low; cover and simmer until the vegetables and wings are falling apart, 30 to 40 minutes. Place the chicken breast and thigh in simmering broth. Cover and cook until a thermometer inserted into the chicken registers 165°F, about 15 minutes. Remove the chicken breast and thigh from the broth. Cool slightly. Refrigerate until needed. Strain the broth through a fine mesh strainer lined with cheesecloth, pressing on the solids. Discard the solids. Pour the broth into a resealable container; stir in the vinegar. Cool completely, about 1 hour. Refrigerate until needed.