I'de take it back and demand it be fixed.
It's not normal. If you buy a new bike, you don't want the headlight fogging up inside. Obviously it can make the already bad headlights a little worse, but it just looks bad...and on a new/newer bike that's still under warranty.
The fact is, most dealerships really suck and don't want to do anything more than they have to.
I've ridden ALL my bikes many times in 100% humidity, dense fog, all temperatures, ect., and I've never had a headlight fog.
The light housing itself simply isn't sealed properly.
If it wasn't under warranty, I'de bake it in the oven for about 10 minutes on the lowest setting.
That won't harmm the light, but it will soften the plastic just enough to pop it apart without damaging it.
After it cooled I'de put it back together with a thin bead of clear or black silicone.
Best of luck getting it fixed.