[FEATURE] Extend BatchInference to Work with any TrainerStep output (model agnostic)

[hamzamaiot]

Is your feature request related to a problem? Please describe.
Currently, there is only one evaluator, the TFMAEvaluator. We need to make it work for any upstream Trainer.

Describe the solution you'd like
Exposing an appropriate Step interface should do the trick -> User will be able to define their own Predict logic and their own Write logic to evaluate on any model and write to any sort of database.

Describe alternatives you've considered

Additional context