fix(ops/modules): re-add cheddar highlighting server

This was deleted when removing the Sourcegraph module, but it turns out it is
also needed by panettone.

Change-Id: I8f14165bf783743247894c2b64882fbb032ffbf8
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12295
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

ops/modules/cheddar.nix

@@ -0,0 +1,29 @@
+{ depot, config, pkgs, lib, ... }:
+
+let
+  cfg = config.services.depot.cheddar;
+  description = "cheddar - markdown/highlighting server";
+in
+{
+  options.services.depot.cheddar = with lib; {
+    enable = mkEnableOption description;
+    port = mkOption {
+      description = "Port on which cheddar should listen";
+      type = types.int;
+      default = 4238;
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    systemd.services.cheddar-server = {
+      inherit description;
+      wantedBy = [ "multi-user.target" ];
+      script = "${depot.tools.cheddar}/bin/cheddar --listen 0.0.0.0:${toString cfg.port} --sourcegraph-server";
+
+      serviceConfig = {
+        DynamicUser = true;
+        Restart = "always";
+      };
+    };
+  };
+}