Add UBX-MON-SYS message to Firmware Gen. 9

[bnbhat]

UBX-MON-SYS (0x0A 0x39) message provides system performance information for monitoring purposes. It includes,

• CPU Load
• Memory Usage
• IO Usage
• Uptime
• Warning/Error Counts
• Temperature

Interface definition can be found here

This msg is useful in various testing and monitoring usecases.

I've tested it on ZED-F9P module and it works as expected.