Support TP for save_pretrained()
Author: amd-xiaoyu12
Pull request: yes

# What does this PR do?

When a model is quantized using TP, the save_pretrained() need to support TP when quantization is done and export to model to safetensor file.

The modification will combine the DTensor to full tensor in process which rank = 0 and export the result, for process with other rank number, the exporting task will be skipped.  
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Fixes # (issue)


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Comments:
cc @arthurzucker @Cyrilvallez