Model and former Patriots cheerleader Camille Kostek, who made headlines last spring when she started dating Rob Gronkowski, is joining the on-air team at “Dirty Water TV,’’ the nightlife show on NESN. Kostek’s first gig will be Sunday’s “Beauty Brunch’’ book party for Medford native Maria Menounos, whose latest release is “The EveryGirl’s Guide to Cooking.’’ The party at Gaslight in Lynnfield is open to the public; $40 ticket includes a drink, treats, and a paperback copy of the release.