mlflow-package should have ready examples for predictions for pytorch, tensorflow (both mnist) and xgboost (covertype)

[Zethson]

Currently the mlflow-packages templates for pytorch, tensorflow and xgboost do not really have out of the box working predictions.
Only xgboost works, but it is not using the covertype example and therefore does not match with the general mlflow-xgboost model.

mlflow-package for pytorch should load a trained mnist model and perform a prediction. Maybe even plot one thing.
Same for Tensorflow (mnist) and XGBoost with covertype.

[Zethson]

@emiller88 assigned to you as well for now. This one will come last and will require some more explanation from me.

[Zethson]

@Zethson Let's use a minimal Poetry for this one.