The largest federal transit grant in history, $6.8 billion to build the $16 billion Gateway Tunnel project between New Jersey and New York, has been approved by a federal agency, officials said. The $6.8 billion full funding grant agreement between the Federal Transit Administration and Gateway Development Commission was confirmed Tuesday, and the federal government told Congress it would provide an additional $6.88 billion to the project, according to U.S. Rep. Josh Gottheimer’s office. “After years of hard work, there’s nothing better than seeing federal investment at work to help our famili…