`plant_min_temp` isn't converted from ºC to K by `write.config.xml.ED2()`

### Bug Description

The prior in BETY for `plant_min_temp` is uniform from -100 to 0 (ºC) and I see values around -5 in config.xml files generated by PEcAn.  ED2 defaults for this value are in K though, so this should get converted.  Need to add something in the `convert.samples.ED()` function that is called by `write.config.xml.ED2()`
