By Ezgi Erkoyun, Ece Toksabay and Max Hunder ISTANBUL/KYIV (Reuters) -Russia and Ukraine signed a landmark deal on Friday to reopen Ukrainian Black Sea ports for grain exports, raising hopes that an international food crisis aggravated by the Russian invasion can be eased. The accord crowned two months of talks brokered by the United Nations and Turkey, a NATO member that has good relations with both Russia and Ukraine and controls the straits leading into the Black Sea. Speaking at the signing ceremony in Istanbul, U.N. Secretary General Antonio Guterres said the deal opens the way to signifi…