Added minimal zfs config

Still want to add an option for zfs on root later on.

modules/system/zfs/default.nix

@@ -0,0 +1,22 @@
+{
+  options,
+  config,
+  pkgs,
+  lib,
+  ...
+}:
+with lib; let
+  cfg = config.aa.system.zfs;
+in {
+  options.aa.system.zfs = with types; {
+    enable = mkEnableOption "zfs";
+    # TODO: Introduce a zfsOnRoot option
+  };
+
+  config = mkIf cfg.enable {
+    services.zfs = {
+      autoScrub.enable = true;
+      autoSnapshot.enable = true;
+    };
+  };
+}