What better way for Doen to toast their arrival on the Upper East Side than with a night out for cocktails, caviar and dancing? The California-based brand took over Chez Fifi on Thursday evening to celebrate its new Madison Avenue boutique, the second in Manhattan.   Iris Apatow , Lila Moss, Chloe Fineman , Lily Rabe, Busy Phillips, Ava Phillippe, Phoebe Gates, Jacquelyn Jablonski, Ashley Avignone and more were dressed in the brand’s signature romantic looks as they milled about the two-story restaurant. Dishes of olives and marcona almonds decorated tables while a large display of potato chips and caviar awaited guests at the rear of the restaurant.  Margaret Kleveland and Katherine Kleveland Lexie Moreland/WWD The brand’s founders, sisters Margaret Kleveland and Katherine Kleveland, floated between guests throughout the night.  You May Also Like It was Margaret’s first time at Chez Fifi, but the hot spot had come much recommended by her friends in the know.  “It was a question of…