move out some common host settings to hosts/common.nix

hosts/common.nix

@@ -0,0 +1,31 @@
+{ config, pkgs, ... }: {
+  # Allow unfree packages
+  nixpkgs.config.allowUnfree = true;
+
+  # Set your time zone.
+  time.timeZone = "America/Los_Angeles";
+
+  # Select internationalisation properties.
+  i18n.defaultLocale  = "en_US.UTF-8";
+  i18n.extraLocaleSettings = {
+    LC_ADDRESS        = "en_US.UTF-8";
+    LC_IDENTIFICATION = "en_US.UTF-8";
+    LC_MEASUREMENT    = "en_US.UTF-8";
+    LC_MONETARY       = "en_US.UTF-8";
+    LC_NAME           = "en_US.UTF-8";
+    LC_NUMERIC        = "en_US.UTF-8";
+    LC_PAPER          = "en_US.UTF-8";
+    LC_TELEPHONE      = "en_US.UTF-8";
+    LC_TIME           = "en_US.UTF-8";
+  };
+
+  nix.settings.experimental-features = [ "nix-command" "flakes" ];
+
+  environment.etc."current-system-packages".text =
+    let
+      packages = builtins.map (p: "${p.name}") config.environment.systemPackages;
+      sortedUnique = builtins.sort builtins.lessThan (pkgs.lib.lists.unique packages);
+      formatted = builtins.concatStringsSep "\n" sortedUnique;
+    in
+      formatted;
+}