Ad agency Innocean USA, which creates advertising for Hyundai and others, has agreed to move its U.S. headquarters to El Segundo in one of the largest leases of the year in the South Bay. Seoul-based Innocean will rent 100,000 square feet in a former airplane manufacturing plant that has been converted to offices and now houses well-known businesses such as L’Oréal cosmetics and Beyond, which makes plant protein meat substitutes. Innocean USA is…