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)

[Voldivh]

LGTM, thanks for pushing this @francocipollone just tried out and works as expected! However, for some reason the command to test it did not work and had to write it manually.