ReshardingMetrics getOperationElapsedTime needs to lock

boost::optional<Milliseconds> getOperationElapsedTime() const.

This function was added recently and accesses the runningOperation TimeInterval

https://github.com/mongodb/mongo/blob/fdaf29180e2c4218c99544bf377fc05dcc378fc5/src/mongo/db/s/resharding/resharding_metrics.cpp#L381

without acquiring a lock on _mutex as required by

https://github.com/mongodb/mongo/blob/fdaf29180e2c4218c99544bf377fc05dcc378fc5/src/mongo/db/s/resharding/resharding_metrics.h#L123