By Natalia Zinets and Matthias Williams (Reuters) -As Ukraine braces for a possible attack from Russia, President Volodymyr Zelenskiy said on Saturday he wanted to convene a meeting of world powers to secure new security guarantees for his country as the current global system is no longer fit for purpose. Speaking at the Munich Security Conference, Zelenskiy also called on NATO members to be honest about whether they wanted Ukraine to join the alliance or not. The 44-year-old leader received a standing ovation before starting remarks in which he called on the world to learn the “terrible lesso…