How to enable Avoid ADSB mode?

[qishen]

Hello, I have a use case for the Avoid ADSB flight mode in Ardupilot and it seems that's not in the default FlightMode in MAVSDK. I wonder what's the best practice to use an unsupported flight mode in MAVSDK and would you accept a PR to add a new plugin for Avoid ADSB mode?