Safe Reconfig requires data replication across config versions for liveness reasons.

Currently, we do not sync from a node that has a different config version. The oplog fetcher checks if it should stop fetching from the sync source (after it has fetched the first batch).

shouldStopFetching calls replCoord->shouldChangeSyncSource which finally calls topCoord->shouldChangeSyncSource. Here, we check for the various reasons we would want to change sync source (i.e. not being in the same config).