[Shardformer] Fix Shardformer FP8 communication training accuracy degradation

[GuangyaoZhang]

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🚨 Issue number

resolve #5920

📝 What does this PR do?

Currently the FP8 communication in shardformer will have lower accuracy compared with FP16.

Following NVIDIA's practice. We have e4m3 forward and e5m2 backward.

GPT2 finetune(4GPU)	Acc
FP16	0.755
FP8, e5m2	0.737
FP8, e4m3 forward and e5m2 backward	0.752

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