temperature_sensor: Add get_status() function

Provide printer.<sensor-config-name>.temperature variable to gcode macro
environment

Signed-off-by: Simon Kühling <mail@simonkuehling.de>

klippy/extras/temperature_sensor.py

@@ -22,6 +22,8 @@ class PrinterSensorGeneric:
         self.last_temp = temp
     def get_temp(self, eventtime):
         return self.last_temp, 0.
+    def get_status(self, eventtime):
+        return {'temperature': self.last_temp}
 
 def load_config_prefix(config):
     return PrinterSensorGeneric(config)