Darden Restaurants Inc. is adding another new restaurant concept to its fold nearly three years after unloading the 50-year-old Red Lobster seafood chain. The Orlando-based restaurant firm (NYSE: DRI) on March 27 announced it has agreed to buy Cheddar’s Scratch Kitchen for $780 million in an all-cash deal from its stockholders, which includes private equity firms L Catterton and Oak Investment Partners. Ian Baines, CEO of Cheddar’s, will remain president of Cheddar’s and report to Darden…