Handle exception when importing RetroGPTChunkDatasets

[guyueh1]

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 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

# Add a code snippet demonstrating how to use this 

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Additional Information

• Related to # (issue)

[thomasdhc]

LGTM