The scope is to implement the WiredTiger part 1 of the project oplog durablity:

Part 1:

1. Update the WT_UPDATE and WT_TXN structure to add a new member to store durable_timestamp.
2. As part of commit transaction, copy the given commit_timestamp to durable_timestamp if it is a prepared transaction and durable_timestamp is not specified.
3. Update __rec_txn_read function to check if the session is checkpoint session, if yes make the update visible only if durable_timestamp is earlier than given timestamp.
4. Update the eviction to consider the update as uncommitted if durable_timestamp is less than stable_timestamp.
5. Enforce durable_timestamp rules.
   1. For any prepared transaction, durable timestamp has to be specified.
   2. For any non-prepared transaction, if a durable timestamp is specified, it should be equal to commit_timestamp.
   3. A durable timestamp should be later than stable timestamp.
6. Remove the constraint that a stable timestamp cannot pass past a prepared timestamp.