Task to block until processing of all data records in the parent shard(s) is completed.
We check if we have checkpoint(s) for the parent shard(s).
If a checkpoint for a parent shard is found, we poll and wait until the checkpoint value is SHARD_END
(application has checkpointed after processing all records in the shard).
If we don't find a checkpoint for the parent shard(s), we assume they have been trimmed and directly
proceed with processing data from the shard.