`mqtt` log facility

[bobrippling]

Description

I have errors appearing both for mqtt and update, often duplicates, for example:

[update error] unable to parse poll-read bai PredCombustionPredCounter from 3108b509030d4001 / 00: ERR: invalid position
[mqtt error] decode bai PredCombustionPredCounter: ERR: invalid position

I'd like to silence the mqtt logs but currently cannot, as they're not part of a log facility, just emitted as other:

ebusd/src/ebusd/mqtthandler.cpp

Line 387 in 38db2d2

logOtherError("mqtt", "unable to open integration file %s", g_integrationFile);

Could the mqtt logs be made into their own facility?