Bug: StepSaverCallback & BestModelCheckpoint not working in version 0.7.0

[guillaume-chevalier]

Describe the bug
From version 0.7.0 and later, these callbacks don't have access to the pipeline anymore since the pipeline isn't stored anymore in the TrialSplit, but just in the AutoML class.

To Reproduce
Update to 0.7.0 and run these tests that are skipped.

Expected behavior
Callbacks are supposed to log models using the repo.

Suggested Fix
Possibly have the TrialSplits contain their trained model again, instead of letting the Trainer call the model.

Additional context
0.7.0 is not merged nor deployed at the moment of writing this issue.

[stale]

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