Handle exception when importing RetroGPTChunkDatasets
@JimmyZhang12 could you trigger CICD again, let's get this merged wait, need to resolve a confict The bot pushed some changes to `.secrets.baseline` , not sure if that's normal; please start CICD @JimmyZhang12  @ko3n1g Any idea what the secret baseline update is about? > @ko3n1g Any idea what the secret baseline update is about?

I have a bunch what’s going on. I’ll send a fix tmrw  @guyueh1 @ko3n1g merged in the changes to fix the secret update. Let's merge main and revert the secret change in this PR. Should be able to merge after that. Thanks! Reverted the commit that changed .secrets.baseline and merged main, let's see if the "Update baseline" commit comes this time <!-- pylint-output-strict-mode-false -->

beep boop 🤖: 🙏 The following files have warnings. In case you are familiar with these, please try helping us to improve the code base.

---

Your code was analyzed with PyLint. The following annotations have been identified:

```
************* Module nemo.collections.nlp.data.language_modeling.megatron.retro_dataset
nemo/collections/nlp/data/language_modeling/megatron/retro_dataset.py:68:0: C0301: Line too long (218/119) (line-too-long)
nemo/collections/nlp/data/language_modeling/megatron/retro_dataset.py:78:0: C0301: Line too long (172/119) (line-too-long)
nemo/collections/nlp/data/language_modeling/megatron/retro_dataset.py:83:0: C0301: Line too long (150/119) (line-too-long)
nemo/collections/nlp/data/language_modeling/megatron/retro_dataset.py:103:0: C0301: Line too long (140/119) (line-too-long)
nemo/collections/nlp/data/language_modeling/megatron/retro_dataset.py:113:0: C0301: Line too long (156/119) (line-too-long)
nemo/collections/nlp/data/language_modeling/megatron/retro_dataset.py:58:0: C0115: Missing class docstring (missing-class-docstring)
nemo/collections/nlp/data/language_modeling/megatron/retro_dataset.py:127:0: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/nlp/data/language_modeling/megatron/retro_dataset.py:17:0: W0611: Unused import os (unused-import)
nemo/collections/nlp/data/language_modeling/megatron/retro_dataset.py:18:0: W0611: Unused import time (unused-import)
nemo/collections/nlp/data/language_modeling/megatron/retro_dataset.py:20:0: W0611: Unused numpy imported as np (unused-import)
nemo/collections/nlp/data/language_modeling/megatron/retro_dataset.py:22:0: W0611: Unused DictConfig imported from omegaconf.dictconfig (unused-import)
nemo/collections/nlp/data/language_modeling/megatron/retro_dataset.py:24:0: W0611: Unused get_datasets_weights_and_num_samples imported from nemo.collections.nlp.data.language_modeling.megatron.base_dataset_utils (unused-import)
nemo/collections/nlp/data/language_modeling/megatron/retro_dataset.py:24:0: W0611: Unused get_train_valid_test_split_ imported from nemo.collections.nlp.data.language_modeling.megatron.base_dataset_utils (unused-import)
nemo/collections/nlp/data/language_modeling/megatron/retro_dataset.py:28:0: W0611: Unused BlendableDataset imported from nemo.collections.nlp.data.language_modeling.megatron.blendable_dataset (unused-import)
nemo/collections/nlp/data/language_modeling/megatron/retro_dataset.py:29:0: W0611: Unused deallocate_indexed_dataset_memory imported from nemo.collections.nlp.data.language_modeling.megatron.indexed_dataset (unused-import)
nemo/collections/nlp/data/language_modeling/megatron/retro_dataset.py:30:0: W0611: Unused make_dataset imported from nemo.collections.nlp.data.language_modeling.megatron.indexed_dataset as make_indexed_dataset (unused-import)
nemo/collections/nlp/data/language_modeling/megatron/retro_dataset.py:35:4: W0611: Unused tensor_parallel imported from megatron.core (unused-import)
nemo/collections/nlp/data/language_modeling/megatron/retro_dataset.py:37:4: W0611: Unused RetroGPTChunkDatasets imported from megatron.core.datasets.retro.config (unused-import)

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Your code has been rated at 7.63/10
```

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Thank you for improving NeMo's documentation! @thomasdhc CICD finished, looks good to merge
# What does this PR do ?

Handle exception during import of RetroGPTChunkDatasets

**Collection**: [Note which collection this PR will affect]

# Changelog 
- Handle Exception during import to allow a graceful fallback when importing RetroGPTChunkDatasets from megatron.

Currently on arm linux platform, `from megatron.core.datasets.retro.config import RetroGPTChunkDatasets` fails with an exception which is [a known issue](https://github.com/facebookresearch/faiss/issues/3936) with its dependency, faiss. When the exception happens, we want to gracefully fall back to the codepath without megatron retro support.

# Usage
* You can potentially add a usage example below

```python
# Add a code snippet demonstrating how to use this 
```

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