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/machines/whitby/default.nix

@@ -11,6 +11,7 @@ in
   imports = [
     (mod "atward.nix")
     (mod "cgit.nix")
+    (mod "cheddar.nix")
     (mod "clbot.nix")
     (mod "gerrit-autosubmit.nix")
     (mod "irccat.nix")
@@ -305,6 +306,9 @@ in
     agentCount = 32;
   };
 
+  # Run Markdown/code renderer
+  services.depot.cheddar.enable = true;
+
   # Start a local SMTP relay to Gmail (used by gerrit)
   services.depot.smtprelay = {
     enable = true;