A Phase 3, randomized, placebo-controlled, double-blind clinical study of pembrolizumab (MK3475) with or without lenvatinib (E7080/MK-7902) to evaluate the safety and efficacy of pembrolizumab and lenvatinib as 1L intervention in a PD-L1 selected population of participants with recurrent or metastatic head and neck squamous cell carcinoma (R/M HNSCC) (LEAP-010)