add jaas configuration field

[MikeKemmerer]

Please add a jaas configuration field so that if the jaas file contains secrets, it can be stored in the secrets keystore. Or, as another possibility, please add support to put variables in the jaas file that are then populated with values in the secrets keystore.

Is this possible by using sasl.jaas.config from org.apache.kafka.common.config.SaslConfigs?