Add ignore_id/pad_id for classification Acc and sCELoss for seq of label models
- [x] Add `pad_id` for `SmoothedCrossEntropyLoss` to ignore label=pad_id in labels. In most cases pad_id is max_label+1.
Handel general cases, and special case that has padding label e.g. 5, but the model output of shape pad_id, e.g. [0,1,2,3,4]
- [x] Add `ignore_id` for `TopKClassificationAccuracy` to Ignore label=ignore_id in labels and corresponding indices in predictions. Typically used for excluding padding_id.
- [x] Add tests for `TopKClassificationAccuracy`
- [x]  Add tests for  `SmoothedCrossEntropyLoss`

Signed-off-by: fayejf <fayejf07@gmail.com>