Infer pretrained base model and tokenizer used from a fine-tuned model_dir
### Feature request

I would like to infer the pretrained base model and the tokenizer from the model_dir of a fine-tuned model. Is that possible with the default trainer setup? What I did previously was to programmatically copy all the tokenizer data into each checkpoint folder. But this seems cumbersome. 

### Motivation

This reduces overhead during inference/prediction. All I have to specify is just the model_dir. 

### Your contribution

Given enough guidance, I am happy to submit a PR.
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