change: add PyTorch configuration for image_uris.retrieve()

[laurenyu]

Issue #, if available:
#1464

Description of changes:
I copied the unit test logic from MXNet to handle the MMS split.

Testing done:

• unit tests
• --collect-only with integ tests to verify fixtures

Merge Checklist

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General

• I have read the CONTRIBUTING doc
• I used the commit message format described in CONTRIBUTING
• I have passed the region in to all S3 and STS clients that I've initialized as part of this change.
• I have updated any necessary documentation, including READMEs and API docs (if appropriate)

Tests

• I have added tests that prove my fix is effective or that my feature works (if appropriate)
• I have checked that my tests are not configured for a specific region or account (if appropriate)
• I have used unique_name_from_base to create resource names in integ tests (if appropriate)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[sagemaker-bot]

AWS CodeBuild CI Report

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• Commit ID: e89ecc6
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AWS CodeBuild CI Report

• CodeBuild project: sagemaker-python-sdk-notebook-tests
• Commit ID: 75b46db
• Result: SUCCEEDED
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AWS CodeBuild CI Report

• CodeBuild project: sagemaker-python-sdk-zwei-pr
• Commit ID: 75b46db
• Result: SUCCEEDED
• Build Logs (available for 30 days)

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AWS CodeBuild CI Report

• CodeBuild project: sagemaker-python-sdk-local-mode-tests
• Commit ID: 75b46db
• Result: SUCCEEDED
• Build Logs (available for 30 days)

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[metrizable]

looks good to me