See if a specialized trainer supporting pre_fit for cli/etc. is feasible

[jlperla]

From mauricio on slack:

Just in case you find it useful I give a different idea which I would probably take if doing something like this. Note that LightningCLI can receive as input the trainer_class. The reason for this is for users to be able to extend the lightning trainer class when needed. A possibility could be to extend the fit method such that internally it would do some pretraining (disabling callbacks and loggers) and then call super().fit(). Another possibility would be to have a new method e.g. pre_fit which would implement this. Then the user would call first pre_fit and then fit. The reason why I would tend to go this way is that this fits more as training logic than cli logic