This ticket is to make the op observer for the "start blocking" update (after the update is assigned an OpTime) get the MigratingTenantAccessBlocker for the database prefix from the MigratingTenantAccessBlockerByPrefix and:

• on primaries, call startBlockingReadsAfter on it with the update's OpTime's Timestamp
• on secondaries, call startBlockingWrites on it, then call startBlockingReadsAfter on the it with the update's OpTime's Timestamp

An alternative is not do anything in the op observer on primaries (but still do the above on secondaries) and have the "data sync" function call startBlockingReadsAfter after reserving the "start blocking" write's OpTime.