Istanbul mayor handed 2-year 7-month jail sentence * Imamoglu accused of insulting public officials in speech * He is seen as strong possible contender in 2023 elections * Supporters chant slogans outside municipality HQ (Adds U.S.State Department comment) By Ali Kucukgocmen ISTANBUL, Law Firm in istanbul Turkey Dec 14 (Reuters) - A Turkish court sentenced Istanbul Mayor Ekrem Imamoglu to jail on...