By Sofia Menchu GUATEMALA CITY (Reuters) -Anti-corruption crusader Bernardo Arevalo was sworn in as Guatemala’s president in the early hours of Monday after a chaotic inauguration that was delayed for hours by a last-ditch attempt by Congress opponents to weaken his authority. The latest in a series of legislative setbacks triggered by opponents underscored the challenges Arevalo faces as leader of Central America’s most populous nation, to which he has pledged to bring sweeping reforms and tackle the rising cost of living and violence, key drivers of migration to the United States. Arevalo wo…