Swapped inputs in decoder onnx file
It appears the transformer decoder when exported to onnx has swapped the `encoder_mask` and `encoder_embeddings`:

```python
encoder_mask : ['encoder_mask_dynamic_axes_1', 'encoder_mask_dynamic_axes_2', 1024]
encoder_embeddings : ['encoder_embeddings_dynamic_axes_1', 'encoder_embeddings_dynamic_axes_2']
```

You can obtain the above output with the following code snippet (used MT as that is my use case, but assume it would be the case for any decoder.)

```python
from nemo.collections.nlp.models.machine_translation.mt_enc_dec_model import MTEncDecModel
import onnxruntime as rt

mt_model = MTEncDecModel.from_pretrained('nmt_en_de_transformer12x2')
mt_model.decoder.export('decoder.onnx')

decoder_session = onnxruntime.InferenceSession('decoder.onnx')
for i in decoder_session.get_inputs():
        print(f'{i.name} : {i.shape}')
```

** Environment overview (please complete the following information) **
- Environment Location: Docker on Kubernetes
- Method of NeMo install: helm chart using nvcr.io/nvidia/nemo:1.2.0
