client: automatically install podman-compose if podman is installed

ops/nixos/lib/client.nix

@@ -17,5 +17,9 @@ in
       # Enable mDNS resolver/responder by default unless otherwise configured.
       connection.mdns=2
     '';
+
+    environment.systemPackages = with pkgs; lib.mkMerge [
+      (lib.mkIf config.virtualisation.podman.enable [ podman-compose ])
+    ];
   };
 }