PartnerAppAuthProvider class support missing in 3.x (similar to 2.x)

**Describe the feature you'd like**
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PartnerAppAuthProvider is the entity used by Sagemaker Partner AI Apps to use for their apps functionality using sagemaker python sdk.

**How would this feature be used? Please describe.**
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Please see https://github.com/aws/sagemaker-python-sdk/blob/master-v2/src/sagemaker/partner_app/auth_provider.py

**Describe alternatives you've considered**
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N/A

**Additional context**
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Start by reading the referenced master-v2/src/sagemaker/partner_app/auth_provider.py implementation and compare it with the 3.x package structure. Identify the corresponding 3.x location and tests for partner app authentication, then verify that PartnerAppAuthProvider is exposed and supports the documented SageMaker Partner AI Apps use case.

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