This fixes two unreleased bugs:

1. Prediction value type of `number` might show unexpected classes

Analytics created models may have class labels like `1, 5, 10` (or some collection of discrete, whole numbers). These labels are passed to the inference model config in the `classification_labels` field.

When the predicted value format is `numeric` it should attempt to see if the classification labels are provided and are numeric. If so, use those. If not, use the underlying value.

2. When supplying an update overwrite, inference was losing the default prediction field value. This is because it was not copied over in the copy ctor in the ClassificationConfig.Builder class. 

closes elastic#55332