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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**Additional context**
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Inizia leggendo l’implementazione di riferimento in master-v2/src/sagemaker/partner_app/auth_provider.py e confrontala con la struttura del pacchetto 3.x. Individua la posizione corrispondente e i test per l’autenticazione delle app partner in 3.x, quindi verifica che PartnerAppAuthProvider sia esposto e supporti il caso d’uso documentato di SageMaker Partner AI Apps.

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