fix: security update -> use sha256 instead of md5 for file hashing

[brockwade633]

Description of changes:
This change updates the sagemaker workflow hashing algorithm from md5 to the more modern sha256

Testing done:
Existing tests will verify backwards compatibility and ensure expected behavior.

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• I have read the CONTRIBUTING doc
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Tests

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[brockwade633]

I amended the same commit locally for cleanliness but unfortunately still ended up with multiple commits here