Modularize nix config

hosts/common/default.nix

@@ -0,0 +1,8 @@
+{ ... }:
+{
+
+  imports = [
+    ./nix.nix
+  ];
+  
+}

hosts/common/nix.nix

@@ -0,0 +1,18 @@
+{ config, pkgs, ... }:
+{
+
+  nix = {
+    gc = {
+      automatic = true;
+      dates = "weekly";
+      options = "--delete-older-than 7d";
+    };
+    settings = {
+      experimental-features = [ "nix-command" "flakes" ];
+      auto-optimise-store = true;
+      trusted-users = [ "jhemono" ];
+    };
+    channel.enable = false;
+  };
+
+}