Enable uploading metrics and upload Test Reordering metrics to dynamodb (#102691)
Added a feature to upload test statistics to DynamoDB and Rockset using a new function `emit_metric` in `tools/stats/upload_stats_lib.py`.
Added metrics to measure test reordering effectiveness in `tools/testing/test_selections.py`.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/102691
Approved by: https://github.com/malfet
