To allow the RecoveryUnit to open a snapshot on the kMajorityCommitted and kLastApplied ReadSource's, we need to implement a snapshot manager for ephemeralForTest.
The replication subsystem hooks into the snapshot manager of the storage engine to update the majority committed and last applied timestamps on the fly.
This should end up looking similar to WiredTiger's snapshot manager implementation.
This ticket should also implement the kNoOverlap ReadSource in ephemeralForTest's RecoveryUnit. The no overlap timestamp is the minimum of the 'all durable' and 'last applied' timestamps.
Enable SnapshotManagerTests for ephemeralForTest