Add an setting for change the height of the dark sky of the void

Since the snapshot 20w49a we can change the height limit of the world and it's awesome! Now we can modify the "min_y" below than zero and it is great! but we always have the dark sky effect of the void starting from the layer 0 without any possibility to move the starting layer of that effect. I think it is possibility now for the developer team to add that option into the game for adding more possibilities in the game.