Cetuximab Recruiting Phase 2 Trials for Clinical Stage III HPV-Mediated (p16-Positive) Oropharyngeal Carcinoma AJCC v8 / Pathologic Stage III HPV-Mediated (p16-Positive) Oropharyngeal Carcinoma AJCC v8 / Pathologic Stage IV HPV-Mediated (p16-Positive) Oropharyngeal Carcinoma AJCC v8 / KRAS Protein Variant / Clinical Stage IV HPV-Mediated (p16-Positive) Oropharyngeal Carcinoma AJCC v8 Treatment