KafkaIO should support dynamic addition of Kafka partitions to assigned topics. #17929
Description
Kafka topics may add partitions dynamically (doesn't require Kafka to restart, or halt a topic), and the KafkaIO should probably support this.
Note:
Consistently assigning partitions should be taken into account, specifically for the case of reading from multiple topics, where one (or more) of the topics added partitions while the pipeline is running.
Imported from Jira BEAM-727. Original Jira may contain additional context.
Reported by: amitsela.