Add a Tutorial Notebook for Data Valuation

[mmschlk]

Add a tutorial notebook showing how shapiq can be used in the context of data valuation.

This notebook should explain how the data valuation problem can be framed as a cooperative game and how shapiq can then be used on this game to get some insights for this game.

An exact computation can be done for a small example and an approximation for a larger one. Runtime for tests would be problematic as the models are retrained.