refactor: share rialo user as a reusable nixos module

Extract the per-host rialo user definition into a Snowfall module
(metacfg.user.rialo.enable) so it can be shared across hosts instead of
copy-pasting the file. Enable it on both amd and x1.

modules/nixos/user/rialo/default.nix

@@ -0,0 +1,34 @@
+{
+  config,
+  pkgs,
+  lib,
+  ...
+}:
+with lib;
+with lib.metacfg;
+let
+  cfg = config.metacfg.user.rialo;
+in
+{
+  options.metacfg.user.rialo = with types; {
+    enable = mkBoolOpt false "Whether or not to enable the rialo user.";
+  };
+
+  config = mkIf cfg.enable {
+    users.users.rialo = {
+      isNormalUser = true;
+      home = "/home/rialo";
+      group = "users";
+      shell = pkgs.bash;
+      uid = 1001;
+      extraGroups = [
+        "wheel"
+        "docker"
+        "dialout"
+        "tss"
+      ];
+    };
+
+    nix.settings.trusted-users = [ "rialo" ];
+  };
+}