The goal of this task is to understand how batched insertions/deletions on the donor shard affect the migration catch up phase.

More specifically, recently we got two BFG-1172094, BFG-1172896 (part of BF-25179) that showed that under the presence of batched deletions the catch-up phase on the recipient didn't manage to converge with 37.5s.

Apart from that, it is interesting to point out that even if the migration is aborted, when we are applying the changes on the recipient we only check whether the migration was aborted between batches. In these two BFGs, there was just one batch but had 100K docs, so it took a lot of time to abort the operation.