[feature request] layout engines - allow passing more options

[mfit]

It would be great if it was possible to pass more options ans configuration through to the layout engines.

For instance, I would like to set the merge edges option for the ELK layout engine.

I see that there are a few available options for the elk engine specifically - so these could be extended to feature mergeEdges - but what about a way to simply pass an arbitrary object / structure to the layout engine, so that any and all settings could be changed (without having to explicitly pipe options through the d2 and to the layout engine) ?