Add support for indictrans2

### Model description

With the recent support for custom models, is it possible to run [IndicTrans2](https://huggingface.co/ai4bharat/indictrans2-en-indic-dist-200M) . It is basically nllb with a custom tokenizer.

### Prerequisites

- [X] The model is supported in Transformers (i.e., listed [here](https://huggingface.co/docs/transformers/index#supported-models-and-frameworks))
- [X] The model can be exported to ONNX with Optimum (i.e., listed [here](https://huggingface.co/docs/optimum/main/en/exporters/onnx/overview))

### Additional information

_No response_

### Your contribution

None, no idea of whether the custom tokenizer is required on js side or nllb tokenizer is fine.