Readd allow_dark_preference_with_rfp.patch

Hey,

not much of an issue, more like a feature request.

I use https://gitlab.com/librewolf-community/browser/source/-/blob/main/patches/removed-patches/allow_dark_preference_with_rfp.patch still to this day, compiling librewolf with this patch from the AUR source.

The AUR source switched over to using the librewolf source releases so it became much harder to patch the source. Still possible though, but I thought it would be about time to talk about adding this patch back as an option switch in the librewolf settings.

There is already a couple of other settings regarding RFP, so this could land amongst them.

I could prepare a MR regarding this, but I'm sure I'll find people opposing it so here's the place about a healthy debate. As for me, I've yet to see a compelling argument against it.