Release only gazebo_msgs on Jazzy

[j-rivero]

Gazebo Classic is currently not available on the platforms supported by ROS 2 Jazzy (mainly Ubuntu Noble) and EOL in the next moth of January 2025 so the new release of this whole repository have little sense with this context.

However there is interest into having the gazebo_msgs release out for ROS 2 Jazzy since this "Gazebo" messages can be used a "simulation" messages by other simulations in the ROS ecosystem, OC3D for example. While the optimal solution would be to create a simulator neutral package for messages, the release of gazebo_msgs (with a warning message to avoid new Gazebo users to use them) can facilitate migrations.

//cc @azeey @adamdbrw

[j-rivero]

Released https://index.ros.org/p/gazebo_msgs/github-ros-simulation-gazebo_ros_pkgs/#jazzy