Support for multi robot simulation

[francocipollone]

🎉 New feature

Related to #50

Summary

• Adds support to multi robot

Pendings:

• [ ] Resolve TODOs
• [ ] Update documentation

Test it

  ros2 launch andino_gz andino_gz.launch.py robots:="
       andino1={x: 0.0, y: 0.0, z: 0.1, yaw: 0.};
       andino2={x: -0.4, y: 0.1, z: 0.1, yaw: 0.};
       andino3={x: -0.4, y: -0.1, z: 0.1, yaw: 0.};
       andino4={x: -0.8, y: 0.2, z: 0.1, yaw: 0.};
       andino5={x: -0.8, y: -0.2, z: 0.1, yaw: 0.};
       andino6={x: -0.8, y: 0.0, z: 0.1, yaw: 0.};"

Note: You can add as many as you want

Checklist

• [ ] Signed all commits for DCO
• [ ] Added tests
• [ ] Added example and/or tutorial
• [ ] Updated documentation (as needed)
• [ ] Updated migration guide (as needed)