Multiple UAVs with different firmware in SITL

@Jaeyoung-Lim

I would like to ask about the possibility to spawn multiple UAVs in the same Gazebo simulation with different firmware.

For example, UAV#1 uses custom PX4 firmware A, but UAV#2 uses custom PX4 firmware B.

Because right now, I found only the script to run multiple UAVs with the same PX4 firmware.

Thank you.