pass init_model to lightgbm

```
→ A | warning: The following argument(s) are guarded by bonsai and will not be passed to LightGBM: init_model
There were issues with some computations   A: x55
```

In my current model, I need to boost from an initial model because the prior model has a ton of information I want to include in my final model. I am curious why `init_model` can't be passed to lightgbm.