FR: Report artifacts from Optuna studies via MlFlow

[stroblme]

Is your feature request related to a problem? Please describe.
Currently results of the Optuna studies can only be accessed via Optuna-Dashboard and are therefore hard to extract.

Describe the solution you'd like
Report the results as plotly figures via the available api here as mlflow artifacts.

Describe alternatives you've considered
Store data directly via MlFlow but that would cause unnecessary redundancy. If we would need to access the data directly the effort justifies making some short queries to the Optuna SQL database directly.

Additional context
N/A

[stroblme]

Implemented by adding a log_study method and optuna_selected_parallel_params / optuna_selected_slice_params for the parallel coordinates and slice plots respectively.
This method also sets the study name according to the optuna study, and plots the optimization history and intermediate values.
Currently this method is being called within the minimize node and should be moved to a separate node in the near future.