[Fix] Update reviewId to prNumber

[dcshzj]

There are some parts of the codebase that uses reviewId to query a particular entry in the ReviewRequests table. This is not ideal, as a review request should be identified by the composite primary key of the site name and the pull request number found on GitHub. The reviewId should only be used within the database, or when the siteName and prNumber information is not available.

The URLs used on both the frontend and backend uses the pull request number. Any instances that uses this information should be renamed to prNumber so that it is clearer.