Adds API endpoint to allocate stock items against a SalesOrder

- SalesOrderAllocations are no longer created manually
- API endpoint performs data validation
- Multiple line items can be allocated at once
- Adds unit testing for new API endpoint

InvenTree/build/serializers.py

@@ -422,7 +422,7 @@ class BuildAllocationSerializer(serializers.Serializer):
         Validation
         """
         
-        super().validate(data)
+        data = super().validate(data)
 
         items = data.get('items', [])