created system module

modules/system.nix

@@ -0,0 +1,28 @@
+{...}: {
+  nix = {
+    settings = {
+      experimental-features = ["nix-command" "flakes"];
+    };
+    gc = {
+      automatic = true;
+      dates = "weekly";
+      options = "--delete-older-than 7d";
+    };
+    optimise = {
+      automatic = true;
+      dates = ["weekly"];
+    };
+  };
+
+  services = {
+    openssh = {
+      enable = true;
+      ports = [22];
+      settings = {
+        PasswordAuthentication = false;
+        UseDns = true;
+        X11Forwarding = false;
+      };
+    };
+  };
+}