Provide a tool to diagnose network setup issues

[azeey]

Desired behavior

Many new users run into problems using Gazebo due to improper network configuration. It would be great if we can provide a tool to diagnose the problem. As a first step, we can provide a tool like https://docs.ros.org/en/rolling/How-To-Guides/Installation-Troubleshooting.html#enable-multicast that checks if there is a UDP multicast problem blocking discovery.

Alternatives considered

n/a

Implementation suggestion

This could be a gz command.

Additional context

Related issues: https://github.com/gazebosim/gz-sim/issues/1879 https://github.com/gazebosim/gz-sim/issues/2285