Changes
## Improvements
- Added OAUTHBEARER support. New methods: RdKafka\Conf::setOauthbearerTokenRefreshCb(), RdKafka::oauthbearerSetToken(), RdKafka::oauthbearerSetTokenFailure() (#546, #547, @cb-freddysart, @scorgn)
- Added incremental rebalance support. New methods: RdKafka\KafkaConsumer::incrementalAssign(), RdKafka\KafkaConsumer::incrementalUnassign() (#541, @ikeberlein)
- Added RdKafka::getControllerId() (#554, @qkdreyer)
## Bugfixes
- Add private constructor on Metadata classes (#531, @arnaud-lb)
## Other Changes
- Improve KafkaErrorException message (#555, @arnaud-lb)