add retries to external contribution data upload (#100889)
Adds retries to external contribution upload as it is shown to be flaky
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### <samp>🤖 Generated by Copilot at 43c2602</samp>
Added a function to read data from S3 objects and used it to implement a retry mechanism and verification for uploading external contribution stats. Modified `tools/stats/upload_external_contrib_stats.py` and `tools/stats/upload_stats_lib.py`.
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### <samp>🤖 Generated by Copilot at 43c2602</samp>
> _We'll upload the stats to the cloud, me hearties_
> _We'll use `read_from_s3` to check them all_
> _We'll retry if the connection fails, me hearties_
> _We'll log the results and have a ball_
Pull Request resolved: https://github.com/pytorch/pytorch/pull/100889
Approved by: https://github.com/huydhn
