Spawn Helper Option: place entities on `info_node`s

**Suggested by:** epicplayer40

The goal of this option is to help spawned NPCs's pathfinding by spawning them in navigable areas.

This could be achieved by either snapping preview entities on foreign `info_node`s or by passing this option in the spawner structure and to change its spawn position at "run time" (in function `vkx_entspawner.run_spawner`).

I prefer the first option as it shows to the user what does that option do