Add kinova Link6

[anashoussaini]

Description

Added Kinova Link6 robot

Fixes:

Checklist

Please check off each item ([x]) once complete, or mark it as [N/A] if it doesn't apply:

• Added your name to CONTRIBUTORS.md (alphabetically by first name)
• Updated CHANGELOG.md:
  • Global changelog (if your change affects the overall repo)
  • Model-specific changelog (if it affects a specific model only)
• Followed the XML formatting/style guidelines (if editing MJCF)
• Ran pytest test/ locally and ensured all tests pass
• Signed the Contributor License Agreement (CLA)

Refer to the contributing guide if you're unsure about any of the steps.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[louislelay]

Not sure the MuJoCo Menagerie maintainers will accept this PR if it comes from a private repository and isn’t officially recognized by the company. If you already have a working ROS package, maybe check with Kinova to see if they’d like to support it themselves and use yours as a base or inspiration?

[kinovajon]

The private URDF menitoned by @anashoussaini is a Kinova internal URDF. He is working with us on these pull requests.
thanks!