bug: nix store gc deletes many of the initial nix store

Create a symlink to gcroots or do some profile magic. Issue is that the pkgs.buildEnv results are getting copied, not the derivation itself, so there is no easy way to symlink that to the gcroots

Maybe do it like here? https://github.com/NixOS/nix/blob/b89eca9aecc69d4dfc0f0afd9353c126eb7b5858/docker.nix