feat: load checkpoint

[surana01]

The code does not currently support loading from a checkpoint. To add this functionality, we would need to modify the surrogate config file by adding an extra argument, load_checkpoint.

if load_checkpoint != null:
    model = load_model(load_checkpoint)

The load_checkpoint argument contains the name of the checkpoint which will be downloaded from HuggingFace.

[PDuckworth]

@surana01
Please also update the readme with the required config changes necessary to load a checkpont.
Along with an example of how to use a checkpoint model for inference only.