By Akash Sriram and Abhirup Roy (Reuters) -Rivian stuck to its forecast of achieving gross profit in the fourth quarter even as it reported its first drop in quarterly revenue hurt in part by shortage of a component. Shares of Rivian (NASDAQ:) rose nearly 2% as the Irvine, California-based company expects to “generate modest positive gross margin” in the current quarter helped largely by cost cuts, and higher revenue per