equip etrecord class with save method (pytorch#13027)

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ghstack PR number: pytorch#12978 by
@Gasoonjia
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https://github.com/pytorch/executorch/tree/gh/gasoonjia/29/base
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Merge bot PR base: https://github.com/pytorch/executorch/tree/main
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Co-authored-by: gasoonjia <[email protected]>

Author: 2 people