racecar_analytics subscribe mqtt handlers with byte decoding

main.go

func SubscribeECU() {
	Client.Subscribe("ingest/ecu", 0, func(client mqtt.Client, msg mqtt.Message) {
		ecu := ECUFromBytes(msg.Payload()) // add this
		fmt.Printf("[MQ] Received ecu message: %v\n", ecu)
	})
}

func SubscribeBattery() {
	Client.Subscribe("ingest/battery", 0, func(client mqtt.Client, msg mqtt.Message) {
		battery := BatteryFromBytes(msg.Payload()) // add this
		fmt.Printf("[MQ] Received battery message: %v\n", battery)
	})
}