I'm not sure if this is genuinely the case, but fro the CI logs it seems
to me that nur-combined does not actually get used when evaluating
repositories, which was an assumption that I previously had. The current
addition tries it's best to resolve the issue of default.nix not
refering to a local path, but to a derivation in the nix store.
Currently, only gitlab and github links are supported, as smaller git
hosts do not get special treatment from nixpkgs, and thus their
derivation name is not "source"
There might be an issue in CI where the nur-combined directory does not
get cloned. To remedy this, we pass the url of a repos.json element to
the indexing function, with as goal resolving the "pkgs" prefix, as it
seemed to come up quite often. There are some other prefixes that I
haven't figured out yet, but at least this is a start
