What kind of manifest does NEST require?
Hi! I want to train my own pretrained Fast-Conformer model using the NEST framework, but I'm not sure what structure I need for this script: [masked_token_pred_pretrain.py](https://github.com/NVIDIA/NeMo/blob/main/examples/asr/speech_pretraining/masked_token_pred_pretrain.py). Additionally, I don't know what type of validation dataset (validation_ds) I need if the data is unlabeled. Please help me figure this out!