hosts: move nix settings to its own file

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

hosts/programs/nix/default.nix

@@ -0,0 +1,29 @@
+{ self, ... }:
+{
+  nixpkgs = {
+    config = {
+      allowBroken = true;
+      allowUnfree = true;
+    };
+    overlays = [
+      self.overlays.default
+    ];
+  };
+
+  nix = {
+    extraOptions = ''
+      experimental-features = nix-command flakes
+    '';
+    settings = {
+      auto-optimise-store = true;
+      trusted-users = [ "root" "@wheel" ];
+      substituters = [
+        "https://nix-community.cachix.org"
+        "https://mirrors.tuna.tsinghua.edu.cn/nix-channels/store"
+      ];
+      trusted-public-keys = [
+        "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
+      ];
+    };
+  };
+}