Adding MaMUJOCO to benchmarl

Hey team,

I see that you've included the pettingzoo environments, how do you think one should go about to include the MaMUJOCO environments from here:

https://robotics.farama.org/envs/MaMuJoCo/index.html

Review the existing PettingZoo environment integration in BenchMARL, then compare its approach with the MaMuJoCo environments described at the linked Farama documentation. Identify the integration points and requirements for adding MaMuJoCo support; done should be a concrete, agreed implementation path or completed support, but the issue does not name files or tests.

Written by the indexing model from the issue text.