DONALDSONVILLE — A $5.8 billion Hyundai Steel Mill is reshaping life in Donaldsonville, where small businesses are expanding and new residents are moving in.For-rent signs, coming-soon banners, and a packed lunch rush paint a clear picture of how the city has changed since Hyundai announced it would build the steel mill there.Lewis Savoie runs the Cane Sugar Toffee Company — a coffee shop, bakery and lunch spot. He has expanded to keep up with a…