This feature will add a stage field to a review request that will provide some 

context as to where a review request is in its development/review lifecycle. 

This field provides visual information that will aid decision making on a 

review request like whether to perform an automatic code review or wait for 

the author to make changes.
This feature adds built-in stages which are

- ApprovedStage

- CompletedStage

- DiscardedStage

- PendingChangesStage

- PendingReviewsStage

- UnpublishedStage

- WIPStage

All tests pass