Add `AntMaze_*-v5` environments, featuring support for loading Third party robot models to Maze

[Kallinteris-Andreas]

Description

new xml_file argument adds the ability to load robot, that can be loaded with gymnasium/mujoco environments

example with Skydio X2 drone:

env = gymnasium.make('AntMaze_UMaze-v4', xml_file="/home/master-andreas/gym/maze_new/mujoco_menagerie/skydio_x2/scene.xml", max_episode_steps=100, max_geom=100000)

example with Unitree go2 quadruped:

env = gymnasium.make('AntMaze_UMaze-v4', xml_file="/home/master-andreas/gym/maze_new/mujoco_menagerie/unitree_go2/scene.xml", maze_size_scaling=2, maze_height=0.4, max_episode_steps=100)

Type of change

• [ ] Documentation only change (no code changed)
• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [X] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [X] This change requires a documentation update

Checklist:

• [ ] I have run the pre-commit checks with pre-commit run --all-files (see CONTRIBUTING.md instructions to set it up)
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes