(Bloomberg) -- Over the past decade, Sanjeev Gupta has built a reputation as one of the globe’s biggest boosters of steel, sealing a slew of deals for mills and smelters from Romania to Australia -- while racking up billions in debt for moribund assets that few others wanted. The former commodities trader has sketched out a vision of a greener future for steel, with his loose network of companies -- GFG Alliance -- leading the way. But the...