Add Smoke Effect on Enemy Spawn From Relic

[daniela-venuta]

Closes #74

Adds smoke effect and a short delay before enemies spawn to give the player a warning

[daniela-venuta]

works fine.

minor

The smoke effect would look better if it was much shorter (since the enemies are popping into the scene instantly) and possibly make it circular like it's radiating on the floor off of them.

Something like this: https://user-images.githubusercontent.com/35614138/143910210-f3bf7acf-de82-4663-811a-aa9e3e0a7db1.mp4

I'm gonna merge this for now as the duration is a serialized field so we can change this in the editor pretty easily. Can make more circular later