By Jan Strupczewski BRUSSELS (Reuters) – The euro zone’s bailout fund offered on Thursday to use its lending capacity to host a 250 billion euro reserve to provide loans to governments in case of external shocks, as the war in Ukraine creates a new challenge amid already stretched budgets. The proposal by the European Stability Mechanism (ESM), which has a lending capacity of 500 billion euros, is part of a long-standing discussion among euro zone governments whether to create a common pool of money to counterbalance the single monetary policy of the European Central Bank (ECB) and help the 19…