Make caster wheel free to move

[gonzodepedro]

🦟 Bug fix

Fixes #

Summary

Lets caster wheels move, so the robot doesn't buck like a horse

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if it affects the public API)

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[francocipollone]

Hey @gonzodepedro thanks for the contribution.
Let me comment here on why I omitted movement on the caster in the first place.

By changing the joint from fixed to continuous, caster_rotation_link will be attached to a dynamic joint and when using the real robot we won't get a joint_state for that particular joint as it isn't being measured. (The position of the swivel caster is unkown from robot point of view)
This will cause the TF tree to be incomplete and we will notice this by rviz throwing all kinds of warnings and the caster not being shown.

Finally, this swivel caster is expected to be replaced by a ball caster. Given that the swivel causes undesired movement when rotating. So a better alternative would be to add a ball caster in the robot description instead.

[olmerg]

Yes, this is required in the simulation but not in urdf

[olmerg]

About this issue I try to add zero friction in rear_caster_wheel_link but when the robot -0.5 m/s in $v_x$ the issue is not solved

[francocipollone]

Closing this PR in favor of #100