Custom callbacks for Pipeline

[brsnw250]

Description

Add the possibility to implement custom callbacks for different stages in the Pipeline. 
Provide access not only for dataset but for transforms and model as well.
Consider the following places:

1. before fitting transforms
2. before fitting the model
3. after all fit is done
4. before transforms applied on forecast / predict
5. after transforms applied on forecast / predict
6. before inverse transforms applied
7. in the end of Pipeline forecast / predict methods

Example of callbacks with access to datset only: MLForecast

Thoughts

This functionality might be helpful not only for debugging purposes but can also help to cover some utility cases, such as logging or saving predictions.

Related

• No way to check what data went into model / transform #480