Adding truth label to results file + Fix flavour retrieval in plotting

Summary

This MR introduces the following changes

• Note: Unit test files changed! No pipeline will success until this is merged!
• Adding the jet truth labels to the results file produced by evaluate_model.py (Like HadronConeExclTruthLablID)
• Removing error prone flavour retrieval from plotting code. This was based on the order of class_labels (which needed to be similar to the ones in the preprocess/train config, otherwise this would lead to wrong flavour retrieval). Now it is based on the truth labels which are stored in the results file.
• Adding dummy empty label values for plotting. If you only want to plot one model without a model label and only the flavour names, this would produce (at the moment) an error. When no label is given for the model, an empty string is added to the model_labels list to keep the lists dimensionality correct.
• Fixing working point values in the discriminant plots. The x-value was given as label to puma which lead to wrong numbers above the vertical lines.
• Sorting the working points which are to be plotted in the discriminant plot in decreasing order so they are correctly printed when same_height_WP is False.

Conformity

• Changelog entry
• Documentation
• Development guidelines
• Style guides