Update Documentation for PostgreSQL

[williams-jack]

Feature/Problem Description

The documentation for Orca has not been updated since replacing Redis as the queue DB with Postgres. Not only should this change be reflected, but items such as protocol diagrams should also be created and added in order to better illustrate the end-to-end workflow of the entire system.

Solution (Changes Made)

• Data definitions update to reflect most recent changes -- especially the GradingJob definition which no longer relies on Redis.
• End-to-end Protocol Diagrams to explain the system.
• Queue documentation to explain the relationship between Reservations, Jobs, and Submitters.