Replacement for `Models.GPKG`

[AngelFP]

The latest release removes the GPKG model, and suggests using the newer BOTORCH_MODULAR instead (https://github.com/facebook/Ax/pull/2316). However, I am not sure how to build a replacement for GPKG using this approach.

Until now I've used GPKG with the Service API for multifidelity optimization, creating a GenerationStep as follows:

GenerationStep(
    model=Models.GPKG,
    num_trials=-1,
    model_kwargs={
        "cost_intercept": cost_intercept
    },
)

What would be the equivalent way of doing this with BOTORCH_MODULAR? I couldn't figure it out from the examples I saw in the documentation.

Best, Ángel.