Fix loading Img2Img refiner components in `from_single_file`

[DN6]

What does this PR do?

set_additional_components for SDXL refiner based pipelines in from_single_file is breaking because no checkpoint argument is passed in.

This PR

1. Passes in the checkpoint to infer_model_type so that the edm_mean and edm_std checks for Playground type models doesn't fail.
2. Makes checkpoint a required argument for infer_model_type

Fixes # (issue)

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