Add system id to identification in sensorML

Currently we have a bunch of different identifier entries in the sensorML, but we miss the id that is associated with the device, platform or configuration. So we want to add this.

Compare with https://sensor.awi.de/rest/sensors/item/getItemAsSensorML/2597:

<sml:identifier>
<sml:Term definition="http://mmisw.org/ont/ioos/definition/sensorID.html">
<sml:label>uniqueID</sml:label>
<sml:value>2597</sml:value>
</sml:Term>
</sml:identifier>

We could give it different labels (deviceID, platformID, configurationID)