Support OAuthBearer authentication for Google Cloud Managed Service for Apache Kafka

[jovezhong]

Use case

Similar to how we support IAM Role for AWS MSK, we'd like to add the recommended OAuthBearer on GCP, to avoid hardcoding the username/password while creating the Kafka External Stream

Describe the solution you'd like

Add a new type of sasl_mechanism to support GCP Kafka
A Java implementation is available at https://github.com/googleapis/managedkafka

Describe alternatives you've considered

Additional context

https://cloud.google.com/managed-service-for-apache-kafka/docs/authentication-kafka?hl=en#Console