MICHAEL Musto is the most flamboyant of all New York gossipers, and so it is right that he should have a flamboyant book party for his new tome, “La Dolce Musto.” On Tuesday, Musto is having a big bash at Room Service where drag king Murray Hill – “the hardest-working middle-aged man in show biz” – will perform a musical tribute/roast. Susanne Bartsch is bringing her crew of downtown divas including Amanda Lepore and other assorted nightlife denizens and drag queens.