feat(aspen/web/orgExportHTML): allow bringing your own config.el

`configFile` is chosen to match the terminology used in NixOS modules. I
think this is quite useful since you can do a lot via the config file
since you can not only set the HTML export setting via the org file
header, but also through various emacs variables (see
<https://orgmode.org/manual/HTML-specific-export-settings.html>).

Change-Id: If4d66348e3043f62782106e7fd34f5cf5c7071a4
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12651
Reviewed-by: aspen <root@gws.fyi>
Autosubmit: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI

users/aspen/web/orgExportHTML.nix

@@ -8,6 +8,7 @@ opts:
 let
   src = if isAttrs opts then opts.src else opts;
   headline = if isAttrs opts then opts.headline else null;
+  configFile = opts.configFile or ./config.el;
 
   bn = builtins.baseNameOf src;
   filename = elemAt (splitString "." bn) 0;
@@ -37,7 +38,7 @@ runCommand outName { inherit src; } ''
   buildFile() {
     cp "$1" file.org
     ${pkgs.emacs}/bin/emacs --batch \
-      --load ${./config.el} \
+      --load ${configFile} \
       --visit file.org \
       --eval "(progn
         ${escapeDoubleQuotes navToHeadline}