Feature: mavcmd: support MAV_CMD_REQUEST_FLIGHT_INFORMATION

[TSC21]

Related: PX4/PX4-Autopilot#7881

[vooon]

It is not require modification of command plugin, as you can use general ~cmd/long.
Only possible needed part is decoder for some messages.

[TSC21]

Only possible needed part is decoder for some messages.

And that's what should be tackled.