Robots.txt: Facets can be exposed on multiple URLs

If facets are available via multiple URLs, only one URL is added to the robots.txt output. This is a case in the training. We have productfacets on /products (like in the cms demo). For the sake of the canonical link exercise we make the products (and their facets) also available under /archive/products.
Robots.txt only shows one of these URLs, but should include both.