feat(template): stamp ElementDataType on instance attribute overrides

Set existingOverride.ElementDataType and newOverride.ElementDataType from
templateAttr.ElementDataType in both the update and create branches of
SetAttributeOverrideAsync, so the persisted InstanceAttributeOverride row
always carries the element type for later central normalizer use (#93/M3).

src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Services/InstanceService.cs

@@ -172,6 +172,7 @@ public class InstanceService
         if (existingOverride != null)
         {
             existingOverride.OverrideValue = overrideValue;
+            existingOverride.ElementDataType = templateAttr.ElementDataType;
             await _repository.UpdateInstanceAttributeOverrideAsync(existingOverride, cancellationToken);
             await _repository.SaveChangesAsync(cancellationToken);
 
@@ -185,7 +186,8 @@ public class InstanceService
             var newOverride = new InstanceAttributeOverride(attributeName)
             {
                 InstanceId = instanceId,
-                OverrideValue = overrideValue
+                OverrideValue = overrideValue,
+                ElementDataType = templateAttr.ElementDataType
             };
 
             await _repository.AddInstanceAttributeOverrideAsync(newOverride, cancellationToken);