public synchronized void assignFromSubscribedAwaitingCallback(Collection<TopicPartition> fullAssignment,
                                                                  Collection<TopicPartition> addedPartitions) {
        assignFromSubscribed(fullAssignment);
        markPendingOnAssignedCallback(addedPartitions, true);
    }
Change the assignment to the specified partitions returned from the coordinator and mark
them as awaiting onPartitionsAssigned callback. This will ensure that the partitions are
included in the assignment, but are not fetchable or initialize positions while the
callback runs. This is expected to be used by the async consumer.

@param fullAssignment  Full collection of partitions assigned. Includes previously owned
                       and newly added partitions.
@param addedPartitions Subset of the fullAssignment containing the added partitions. These
                       are not fetchable until the onPartitionsAssigned callback completes.
clients/src/main/java/org/apache/kafka/clients/consumer/internals/SubscriptionState.java