nixos/nomad: add extraSettingsFiles option to nomad service (#109761)

nixos/modules/services/networking/nomad.nix

@@ -49,6 +49,17 @@ in
         '';
       };
 
+      extraSettingsPaths = mkOption {
+        type = types.listOf types.path;
+        default = [];
+        description = ''
+          Additional settings paths used to configure nomad. These can be files or directories.
+        '';
+        example = literalExample ''
+          [ "/etc/nomad-mutable.json" "/run/keys/nomad-with-secrets.json" "/etc/nomad/config.d" ]
+        '';
+      };
+
       settings = mkOption {
         type = format.type;
         default = {};
@@ -101,7 +112,8 @@ in
       serviceConfig = {
         DynamicUser = cfg.dropPrivileges;
         ExecReload = "${pkgs.coreutils}/bin/kill -HUP $MAINPID";
-        ExecStart = "${cfg.package}/bin/nomad agent -config=/etc/nomad.json";
+        ExecStart = "${cfg.package}/bin/nomad agent -config=/etc/nomad.json" +
+          concatMapStrings (path: " -config=${path}") cfg.extraSettingsPaths;
         KillMode = "process";
         KillSignal = "SIGINT";
         LimitNOFILE = 65536;