PARIS — Gucci has begun selling new luxury sneaker models labelled "Made in China", a break with its Italian manufacturing tradition that some industry watchers say could undermine the brand's high-end image as it races to win back middle-class shoppers. The move highlights the challenge facing Gucci designer Demna, who must create innovative products while keeping costs under control to attract so-called aspirational shoppers, the bulk of luxury consumers who are more price-sensitive than the super-rich. Demna will present his latest collection at a Milan runway show on Friday (Sept 25). His success is crucial for parent Kering and CEO…