Generate default variant url without parameters

[cboelter]

During the debugging of #2402 I thought a bit about the url generation. In case the current product is the default variant it should be possible to generate a product url without the query parameters. The default variant is still loaded without the parameters. The main benefit of this change would that we have cleaner product url's in the sitemap.xml.

What do you think about that?

[aschempp]

sound reasonable, but not sure if that's worth the effort since only a robot will look at the sitemap.xml? 😅