feat(ops): Add NixOS module for atward

Very standard, nothing fancy.

Change-Id: Ibb286f221a4752abfb62e971b98e9496357040f5
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3090
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

ops/modules/atward.nix

@@ -0,0 +1,31 @@
+{ depot, config, lib, pkgs, ... }:
+
+let
+  cfg = config.services.depot.atward;
+  description = "atward - (attempt to) cleverly route queries";
+in {
+  options.services.depot.atward = {
+    enable = lib.mkEnableOption description;
+
+    port = lib.mkOption {
+      type = lib.types.int;
+      default = 28973;
+      description = "Port on which atward should listen";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    systemd.services.atward = {
+      inherit description;
+      script = "${depot.web.atward}/bin/atward";
+      wantedBy = [ "multi-user.target" ];
+
+      serviceConfig = {
+        DynamicUser = true;
+        Restart = "always";
+      };
+
+      environment.ATWARD_PORT = toString cfg.port;
+    };
+  };
+}