Credit: Susan Mullane-Imagn ImagesAt just 22 years old, Coco Gauff already has two grand slam titles under her belt. And now, she’s going to add two more titles to her portfolio: a pair of documentary films. Tennis Channel recently announced two short documentaries that it will debut ahead of the upcoming US Open: Serve: Fashion & Tennis and The Zina Effect. Both are being executive produced by Coco Gauff and her company, iROC Media Group, along…