MQTT/Sparkplug metric properties

[gaillarddamien]

MQTT/Sparkplug metrics may come with properties, but the driver can not handle them all.

At the moment,

• only a handful of them are processed
• with a few others processed on birth only

Some of our devices publish MQTT/Sparkplug metrics with custom properties that go silently ignored, for they are not expected by the driver.

It would be really helpful if we could:

• keep every metric property somewhere (most likely within the realtimeData document associated with this metric?), including properties that are not known beforehand
• archive them into hist too (something like "valueJson": {"p": {"k1": "v1", "k2": "v2"}}?)