Add initial framework for config

common.nix

@@ -0,0 +1,20 @@
+# Common configuration for all systems
+
+{ config, pkgs, ... }:
+
+{
+    nix = {
+        settings.auto-optimise-store = true;
+
+        # Clean generations older than a week
+        gc = {
+            automatic = false; # Flip this to do it automatically
+            dates = "weekly";
+            options = "--delete-older-than 7d";
+        };
+    };
+
+    nixpkgs.config.allowUnfree = true;
+
+    system.stateVersion = "23.05";
+}