ArduPilot: Set rate to receive SYS_STATUS telemetry

[Luc-Meunier]

As discussed in mavlink/MAVSDK-Proto#373 it seems that ArduPilot requires a request before sending https://mavlink.io/en/messages/common.html#SYS_STATUS telemetry.

Otherwise, we never enter the callback when trying subscribe_health (https://mavsdk.mavlink.io/main/en/cpp/api_reference/classmavsdk_1_1_telemetry.html#classmavsdk_1_1_telemetry_1a093a702abd1370ff97f4d9ebce449942).

PR: #2571