Use mavlink-router in the ground image to merge and split MAVLink telemetry

[JacopoPan]

Before

• 2xN MAVLink streams from the simulation-container to the ground-container on ports 1454x (for ground_system) and 1455x (QGC)

After

• 1xN MAVLink streams from the simulation-container to the ground-container on ports 1654x
• added 1 more instance of mavlink start to PX4-Autopilot/ROMFS/px4fmu_common/init.d-posix/px4-rc.mavlink
• 1 instance of mavlink-routerd in the ground-container combining N streams and splitting them in 2 to ports 18540 (for ground_system) and 14550 (QGC) as if they were all coming from 1 serial telemetry radio

TODO

• re-implement ground_system.cpp to be single threaded in deployment
• combine multiple udp streams into a single stream as with a serial telemetry radio
• test with GND_CONTAINER=false and >10 drones
• test virtual joystick with multiple vehicles
• stress test performance
• test missions

Notes

• reduced simulation/deployment gap
• this makes ground_system single threaded instead of having N threads
• we use mavlink-router instead of mavproxy to be able to support the QGC virtual joystick for multiple vehicles
• it does not impact the Gymnasium RL environment as it does not uses the ground-container