By Christoph Steitz, Essi Lehto and Holger Hansen FRANKFURT/HELSINKI/BERLIN (Reuters) -The German government stepped in to rescue Uniper with a 15 billion euro ($15.28 billion) bailout on Friday after the gas importer became the biggest casualty of Europe’s energy standoff with Russia so far. Under a bailout that is among the biggest in German corporate history, the government will take a 30% stake in Uniper, reducing the ownership of its Finnish parent Fortum to 56% from nearly 80% after weeks of tough negotiations. It will also allow Uniper to start passing on some of the costs of soaring ga…