Currently, the optime generator is only accessed via logOp() and logInsertOps() called via an opObserver.
There is a need for being able to obtain (and reserve) optimes prior to opObservers being run; the work for this ticket will be to thread through an interface for obtaining a new block of OpTimes and providing logInsertOps() with these times.

One such need is for transactions that write multiple oplog entries, such as vectored insert.