Configure managed or self-hosted Nix binary cache

Solutions:
- https://cachix.org/
- https://github.com/zhaofengli/attic
- https://nixbuild.net/
- https://garnix.io/
- https://nixos.org/manual/nix/unstable/package-management/s3-substituter.html
- https://github.com/nix-community/harmonia