By Kate Abnett and Robert Muller PRAGUE/BRUSSELS (Reuters) -The European Union will unveil proposals next week to launch joint gas buying within months and develop an alternative gas price benchmark, but a meeting of EU countries on Wednesday left it unresolved whether the package would include a gas price cap. The 27-country EU is plotting its next move to tame soaring energy prices and shield consumers from surging bills, as Europe heads into a winter of scarce Russian gas, a cost of living crisis and the looming threat of recession. After a meeting of EU energy ministers in Prague, EU energ…