Updates GZBridge to extract the drone name from a drone in a nested S…

[hmer101]

Solved Problem

Allows drones in nested SDF models to be flown in gz simulation. This is important if drones are to be connected for multi-drone load carrying and other applications.

Fixes #21767

Solution

• In GZBridge, extracted the actual drone name from the full nested name.

Changelog Entry

For release notes:

Feature/Bugfix: Allows drones nested in other SDF models to be connected to and flown in gz simulation.
Documentation: Perhaps add clarification to page: https://docs.px4.io/main/en/sim_gazebo_gz/multi_vehicle_simulation.html. 

Alternatives

• Set GZBridge's _model_name parameter to just be the drone name every time GZBridge is initialized.
• Update the classes GZMixingInterfaceESC and GZMixingInterfaceServo to work with nested names.

Test coverage

• Ran single-drone sitl and functions exactly as before. Ran single drone in nested model and functions as expected.
• Simulation testing logs: https://logs.px4.io/plot_app?log=e5bd0ed5-c935-40ff-9b89-2ff85caefbf6

Context

See here for full discussion.

[DronecodeBot]

This pull request has been mentioned on Discussion Forum for PX4, Pixhawk, QGroundControl, MAVSDK, MAVLink. There might be relevant details there:

https://discuss.px4.io/t/multi-tethered-drone-error-matching-flight-task-was-not-able-to-run/32993/5