nixos: create 'modules/nixos' folder

Let's consolidate all modules under one path, so that NixOS,
home-manager, and nix-darwin (if I ever end up using it down the line)
would go under the same folder.

modules/nixos/system/docker/default.nix

@@ -0,0 +1,27 @@
+# Podman related settings
+{ config, lib, ... }:
+let
+  cfg = config.my.system.docker;
+in
+{
+  options.my.system.docker = with lib; {
+    enable = mkEnableOption "docker configuration";
+  };
+
+  config = lib.mkIf cfg.enable {
+    virtualisation.docker = {
+      enable = true;
+
+      # Remove unused data on a weekly basis
+      autoPrune = {
+        enable = true;
+
+        dates = "weekly";
+
+        flags = [
+          "--all"
+        ];
+      };
+    };
+  };
+}