Improvement of eta-utility, in particular eta-x and julia_env, as well as the documentation

When switching from Gym to Gymnasium in the production planning experiment, errors still occurred, especially in the julia Env. The main reason for this is the lack of the new features/changes of stablesbaslines3 in eta-utility. In addition, some improvements in the documents are still included in this merge request.

Breaking changes:

1. Update stablesbaslines3 to v2.2.1.
2. Changes from stablesbaslines3 v2.2.1 adapted to the changes from Gym to Gymnasium in no_vec_env.
3. Add julia_env to the documentation.

New features:

Bugfixes:

1. Delete mode from render func in julia_env as it was introduced during the migration from gym to gymnasium.
2. When calling the learning func, the seed is now set before the setup of the agent.
3. Fix formatting errors in the documentation.
4. Add missing function descriptions.
5. When the step function in the nsga2 agent is called, the class expects five return parameters.