Implement plotting utility for generic predictions

[flo-schu]

• [ ] Implement plotting utility for generic predictions and run it after inference, so with submitting the script on the cluster, all results can be inspected.
• [ ] Implement a default posterior predictions method, which simply plots all observations against their predictions for the different data variables
• [ ] Look at https://arviz-plots.readthedocs.io/en/latest/tutorials/plots_intro.html