LONDON (Reuters) - Ninety minutes after resigning as British prime minister on Thursday, Boris Johnson called Ukrainian President Volodymyr Zelenskiy. He told the Ukrainian leader his people had the UK's unwavering support in its fight against Russia, and said Britain would continue to supply vital defensive aid for as long as needed. "You're a hero, Volodymyr," he said, according to an aide who listened to the call. "In this country,