Increase default num_steps for model runs

Utopia currently models for 3 time steps by default. For most models this does not lead to any interesting outputs, potentially causing new users confusion. For showcasing purposes, it might be nice to increase the default number of steps just enough for models to output plots that do make the model's dynamical range (at least partly) visible.

However, the number of steps should be kept to 3 for pipeline testing purposes.