Change Godot rivet configs to JSON

[AngelOnFira]

Godot really doesn't work nicely with editing yml file, since on save, the indentation changes to spaces, which yml isn't compatible with. It would be better to change docs to suggest using JSON, and have that be the default.

From the Godot repo's issues: godotengine/godot-proposals#6250

[linear]

GDT-123 Change Godot rivet configs to JSON