modules/shared: add nix-daemon

modules/nixos/common/nix-daemon.nix

@@ -1,40 +0,0 @@
-{ pkgs, ... }:
-
-let
-  asGB = size: toString (size * 1024 * 1024);
-in
-{
-  nix = {
-    settings.trusted-public-keys = [
-      "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
-    ];
-
-    settings.substituters = [
-      "https://nix-community.cachix.org"
-    ];
-
-    # Hard-link duplicated files
-    settings.auto-optimise-store = true;
-
-    # auto-free the /nix/store
-    settings.min-free = asGB 10;
-    settings.max-free = asGB 200;
-
-    # users in trusted group are trusted by the nix-daemon
-    settings.trusted-users = [ "@trusted" ];
-
-    # useful for ad-hoc nix-shell's for debugging
-    nixPath = [ "nixpkgs=${pkgs.path}" ];
-
-    gc.automatic = true;
-    gc.options = "--delete-older-than 14d";
-  };
-
-  # Sometimes it fails if a store path is still in use.
-  # This should fix intermediate issues.
-  systemd.services.nix-gc.serviceConfig = {
-    Restart = "on-failure";
-  };
-
-  users.groups.trusted = { };
-}