Add per-extruder preheat controls

These are lifted from the bed preheat controls and are not functional at the moment

plugins/UM3NetworkPrinting/ClusterUM3PrinterOutputController.py

@@ -13,6 +13,7 @@ class ClusterUM3PrinterOutputController(PrinterOutputController):
     def __init__(self, output_device):
         super().__init__(output_device)
         self.can_pre_heat_bed = False
+        self.can_pre_heat_extruders = False
         self.can_control_manually = False
 
     def setJobState(self, job: "PrintJobOutputModel", state: str):