By Vitalii Hnidyi and Jonathan Spicer KHARKIV, Ukraine/ISTANBUL (Reuters) -Russia and Ukraine will sign a deal on Friday to reopen Ukraine’s Black Sea ports, Turkey said, a potential breakthrough that could ease the threat of hunger facing millions around the world as a consequence of Russia’s invasion. Ukraine and Russia are both among the world’s biggest exporters of food, and Ukraine’s ports, including the major hub of Odesa, have been blockaded by Russia’s Black Sea fleet. The halt to grain shipments during the five-month war has caused prices to rise dramatically around the world, and reo…