Add Gazebo Sim support while maintaining Gazebo Classic compatibility

[Copilot]

Implements migration from Gazebo Classic to Gazebo Sim (formerly Ignition Gazebo) following LCAS migration patterns. Both simulators remain functional.

Changes

Package Dependencies (hunter_gazebo/package.xml)

• Added ros_gz_sim, ros_gz_bridge, gz_ros2_control alongside existing Gazebo Classic dependencies

Launch Files

• Added launch_gz_sim.launch.py for Gazebo Sim using ros_gz_sim/gz_sim.launch.py and ros_gz_sim/create spawner
  • Passes sim_gazebo:=sim argument to xacro to load only Gazebo Sim plugin
• Clock bridge added: /clock@rosgraph_msgs/msg/Clock[gz.msgs.Clock
• Controller loading switched from ExecuteProcess to controller_manager/spawner nodes
• Updated launch_sim.launch.py for Gazebo Classic to pass sim_gazebo:=classic argument

Robot Description (hunter_description/description/ros2_control.xacro)

• Added xacro conditional logic with sim_gazebo argument (default: 'classic')
• Gazebo Classic plugin (libgazebo_ros2_control.so) loads only when sim_gazebo:=classic
• Gazebo Sim plugin (libgz_ros2_control-system.so) loads only when sim_gazebo:=sim
• Only one plugin loads at a time - prevents conflicts from simultaneous loading
• Fixed parameter path syntax: $(find ...) → $(find-pkg-share ...)

Documentation

• README updated with both launch options
• Added MIGRATION_GUIDE.md with technical details, plugin selection explanation, and testing checklist

Usage

# Gazebo Sim (recommended)
ros2 launch hunter_gazebo launch_gz_sim.launch.py

# Gazebo Classic (legacy)
ros2 launch hunter_gazebo launch_sim.launch.py

The appropriate plugin loads based on the xacro argument passed by each launch file, ensuring only one simulator plugin is active at a time.

• Fixes migrate hunter_gazebo to the new Gazebo Sim #12

Original prompt

---

This section details on the original issue you should resolve

<issue_title>migrate hunter_gazebo to the new Gazebo Sim</issue_title>
<issue_description>Following guidance in https://github.com/LCAS/aoc_distro/wiki/Migration-to-new-Gazebo implement the transition from Gazebo classic to Gazebo Sim for the hunter_gazebo. Some changes may be required in other ROS2 packages in this repository, but mostly it is about changes to hunter_gazebo.

Whereever possible retain compatibility with Gazebo Classic, and keep the changes small and manageable.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes migrate hunter_gazebo to the new Gazebo Sim #12

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[marc-hanheide]

@LeonardoGuevara @ibrahimhroob

I tried this to retain support for both gazebo classic and new gazebo sim...