refactor wheel publishing
When updating dune-xt as well as dune-gdt, configure of dune-gdt fails since the required updated dune-xt wheel is not yet present. We should thus refactor building a bit
separate builds of dune-xt and dune-gdt in different stages?
publish dune-xt to the gitlab registry inbetween?
configure pip to use this registry to allow dune-gdt to depend on the newly built version?