LONDON, June 15 (Reuters) - Sterling struggled to make headway against the dollar and eased against the euro on Thursday after the European Central Bank raised interest rates to their highest level in more than two decades.At 1300 GMT, sterling was stuck at $1.2661 , but had surrendered earlier gains against the euro, which was up 0.22% at 85.74 pence .The ECB said it expected inflation to hover above its 2% target rate through to 2025 and hinted at more interest rate hikes, even as the euro zone economy lags.The...