By John O’Donnell BERLIN (Reuters) – German officials are quietly preparing for any sudden halt in Russian gas supplies with an emergency package that could include taking control of critical firms, three people familiar with the matter told Reuters. The preparations being led by the Ministry for Economic Affairs show the heightened state of alert about supplies of the gas that powers Europe’s biggest economy and is critical for the production of steel, plastics and cars. Russian gas accounted for 55% of Germany’s imports last year and Berlin has come under pressure to unwind a business relati…