[Ovmsdev] Dcdc converter metrics

If additional metrics are being added for the dcdc converter I suggest including the following as well as temp:

v.c.12v.voltage 14.2V v.c.12v.current 10A v.c.12v.power 0.14kW

For the Leaf I have found the dcdc output voltage, still looking for a current reading to calculate the power output.

Cheers Derek