Allow a method to disable auto block state and item model gen. In datagen

[L-Lawlite]

Allow option to disable Datagen for block state and item model and allow to use vanilla default. It is very annoying to make datagen for things specially when it doesnt even follow vanilla. It is fine to keep this as default but atleast have a option to disable it.

[tterrag1098]

I'm not sure what this is asking for. If you want to use an existing vanilla model, just use it as the parent for the generated model. What is "vanilla default" in this case?