By Pavel Polityuk and Natalia Zinets KYIV (Reuters) -Ukraine will ask U.S. Secretary of State Antony Blinken and Defence Secretary Lloyd Austin for more powerful weapons during an expected visit by the officials to Kyiv on Sunday as the Russian invasion enters its third month. Ukrainian President Volodymyr Zelenskiy said his country would overcome “dark times,” in an emotional address at Kyiv’s 1,000-year-old Saint Sophia Cathedral to mark Orthodox Easter as fighting in the east overshadowed the religious celebrations. The trip by Blinken and Austin, announced earlier by Zelenskiy, would be th…