THE first Norman Mailer Writers Colony Gala will honor novelist Toni Morrison for lifetime achievement and David Halberstam for distinguished journalism. Guests at the Oct. 20 event at Ci priani 42nd, hosted by Tina Brown and David Remnick, will include Mailer’s widow, Norris Church Mailer, his nine chil dren and 10 grandchildren, as well as Salman Rushdie, Diane von Furstenberg and Brett Ratner. The Writers Colony, in Mailer’s Provincetown home, nurtures young talents.