The ReshardingCollectionCloner (1 2), ReshardingTxnCloner, and ReshardingOplogFetcher each use read preference mode "nearest" to choose the nodes within the donor replica set shards to read from. We should expose a way have this read preference be configurable. This will enable better workload isolation between the application and resharding.

We should expose configuring the read preference as a server parameter for ease of backporting. There is some prior art for exposing this configuration as a server parameter in SERVER-38731. The option for resharding should additionally (1) be settable at runtime and not only startup for added flexibility and (2) allow specifying read preference tags and not only the read preference mode if feasible in IDL.