RFC: Refactor Training Routes

[adamjcolvin]

What We Currently Have

In our database, a Trainee has a training route, which is defined as an integer. We have text values for each of those integers, which we use in the code. These constants, and many others related to them like ROUTE_INITIATIVES are defined in an initialiser called training_routes.

We also have a library class called TrainingRouteManager, which is responsible for answering questions like requires_schools?, requires_degree? etc.

Proposal

• Change the training_route column in the database to be a string type instead of an integer type. This will remove the need for any mapping with integers, both on our side and on the data side.
• Move any constants around training routes out of the initialiser and into the Trainee model. This seems like the best place, since the routes are the Trainee's responsibility. We could have a concern on Trainee which has all of these constants, the enum definition itself and any other related logic.
• Change references to constants like TRAINING_ROUTE_ENUMS to Trainee::training_routes or something similar.
• Use the enum convenience methods in place of the TrainingRouteManager where possible.
• Move any remaining logic in the TrainingRouteManager into the new concern.