Support Google JWT Authentication for Pub/Sub Push Subscriptions

[imdhemy]

Description

To ensure the authenticity of incoming Real-Time Developer Notifications (RTDN) from Google Play, we need to support verification of JWT tokens sent by Google Cloud Pub/Sub when using authenticated push subscriptions.

This implementation will follow Google’s recommended approach described here:
👉 https://cloud.google.com/pubsub/docs/authenticate-push-subscriptions

Example

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