Cut xacro dependency & download URDF assets from ClearML

[macmacal]

Description

Basically, together with #48 "resolves" the #43 . At least for the ongoing development with rsl_rl library.

• Removes last ties to the ROS 2 dependencies, by removing automatic URDF file generation with xacro.
• Instead, it relies on pre-generated URDF file + copied 3D models with script from aegis_ros/aegis_description.
• PR also introduces a new utlity script to upload URDF assets to the ClearML, as a dataset...
• ... which ID can be now set as the ENV's robot config to version the robot model with the ClearML server.

Motivation and context

• Removing ties to ROS 2 will help us in fixing depends and encapsulating whole project into training container.

Related PRs

• aegis_description - Launch script to generate stadalone URDF model aegis_ros#95

How has this been tested?

• Manually, on a development laptop
• On the geonosis PC with training simulator

Checklist

• All TODOs in the code have been resolved or linked to a proper issue.
• Code has been (auto)formatted.
• Documentation (e.g., README, CHANGELOG, Wiki) has been updated.
• All automated checks have passed.

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Clickup task: 869bu1x36

[sivral]

Looks good to me.