(Reuters) - Tesla Inc unveiled on Thursday its first-ever pickup truck, a long-awaited expansion to its product line-up that poses a direct challenge to Detroit automakers.At a launch event in Los Angeles, Tesla Chief Executive Elon Musk unveiled a truck that looked like a futuristic armoured vehicle and which he claimed "won't scratch".The truck marks the first foray by Tesla, whose Model 3 sedan is the world's top-selling battery electric car, into pickup trucks, a market dominated by Ford..