By Rachel More and Christoph Steitz MUNICH (Reuters) - German Chancellor Friedrich Merz, formally opening the Munich car show on Tuesday, pledged support for the country's embattled auto sector, calling for innovation to head off threats from China and the United States as well as excessive red tape. Carmakers, Germany's biggest industrial sector, are grappling with the toughest challenge in decades, squeezed by higher U.S. import tariffs, weak demand in Europe, a shift to EVs and a raging price war in C ...