refactor: expose cheddar-about script from cheddar

Any other cgit configuration in depot would need this script wrapper as
well.

Change-Id: Ifa04e1c9de9c925eb3f60c5d3854221ae02ef06c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/5206
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>
Autosubmit: sterni <sternenseemann@systemli.org>

tools/cheddar/default.nix

@@ -9,4 +9,15 @@ depot.third_party.naersk.buildPackage {
     # plus additional languages we care about.
     BAT_SYNTAXES = "${depot.third_party.bat_syntaxes}";
   };
+
+  passthru = {
+    # Wrapper for cgit which can't be told to pass arguments to a filter
+    about-filter = pkgs.writeShellScriptBin "cheddar-about" ''
+      exec ${depot.tools.cheddar}/bin/cheddar --about-filter $@
+    '';
+  };
+
+  meta.targets = [
+    "about-filter"
+  ];
 }