Improve the handling of randomness in documentation notebooks

Currently, some documentation notebooks (e.g. [shapley basic spotify](https://github.com/aai-institute/pyDVL/blob/develop/notebooks/shapley_basic_spotify.ipynb)) do not pass seeds or random number generators when calculating shapley values.

We should go over all documentation notebooks and make sure that best practices for controlling randomness are fulfilled and users can see all places where randomness needs to be handled.