Configure datapacks in Edit World menu

With 1.16, we now have the ability to modify a world's datapacks within the World Creation menu. However, after creating a world, there's no in-game way to modify them anymore. The only way is through the /datapack command, which isn't as intuitive.

Solution: a button on the Edit World screen to go back to the datapack configuration, akin to the one from the world creation.