fix: jazzy/ur simulation dependencies

[RomanRobotnik]

This PR is related to #84. The UR official repo does not support (or not well documented) the use of the arms in Gazebo. For this reason we are including as dependency our own fork of the package: https://github.com/RobotnikAutomation/Universal_Robots_ROS2_Description/tree/fix/gazebo-control-jazzy

This pull request adds new repository dependencies required for the robot description package, ensuring all necessary components are included for simulation and sensor support.

Repository dependency updates:

• Updated robot_description.repo.yaml to add the Universal_Robots_ROS2_Description repository (branch: fix/gazebo-control-jazzy) as a dependency, alongside the existing robotnik_sensors repository.

Documentation updates:

• Updated the README.md file to document the new repository dependencies, providing details about robotnik_sensors and Universal_Robots_ROS2_Description and their respective branches.

[RomanRobotnik]

I will close #84 until we can run it with the official repo

[robert-ros]

The official UR simulation is located in Universal_Robots_ROS2_GZ_Simulation

See UniversalRobots/Universal_Robots_ROS2_Description#273

Please review the corresponding files in Universal_Robots_ROS2_GZ_Simulation

• ur_gz.ros2_control.xacro
• ur_gz.urdf.xacro

In general, I would avoid creating fork branches due to the maintenance overhead. It is preferable to stay as close as possible to the original repositories.

However, if this change is required for planning, it could be accepted.

[RomanRobotnik]

Could you check it @jramos-robotnik ?

[jramos-robotnik]

I checked de files.

First of all, ur_gz.urdf.xacro defines a ur_arm in gazebo without an option of using a link from the robot as parent. The parent is always world.

In another hand, ur_gz.ros2_control.xacro works well as a replacement for ros2_control, which was in our forked repository. Given the preference for using official repositories, I've modified robotnik_description to accept this xacro.