In multi-doc transactions, the catalog write to modify the multikey fields is done in a side transaction on the primary. On the secondary, the multikey write happens with the user operation that causes the field to be set. This makes the writes have different timestamps.

In this ticket, we'll use the oplog entry generated from the side transaction to explicitly replicate the multikey write. Currently, the side transaction generates a no-op oplog entry. We might want to change it to a different type.