If the onlineMovePrimary feature flag is on, begin fetching oplogs when cloning begins using the ReshardingOplogFetcher. The fetcher expects a collection UUID in its constructor, so the recipient should invariant that the list of collections to clone contains only one collection and pass its UUID to the fetcher. The oplogs should be written to a buffer that is dropped at the end of the operation or on failure. Write unit tests if possible to ensure that the integration works (e.g. that things are inserted into the buffer, or even simply that the metrics are incremented), but avoid spending time on mocking out complex parts of the system to do this (ReshardingOplogFetcher already does this in its own unit tests).