Draft: Resolve "Stablebaselines3 integration with gymnasium" (to delete)

Closes #169 (closed)

Breaking Changes:

• It is not possible to specify a separate random seed for the environment in the experiment configuration anymore. ETAx now uses the seed from the "settings" section in the configuration.
• If you are not using ETAx to prepare environments, make sure to call vec_env.seed(seed=config.settings.seed) before resetting the environment for the first time. ETAx will do this automatically.
• gymnasium changes what the step() and reset() functions in a custom environment return. Check the gymnasium documentation when converting environments: https://gymnasium.farama.org/api/env/#gymnasium.Env.step.