Add the REST API routes to instance properties

### User Story

As a developer I want the REST API routes added to the instance properties so that they are not hard coded int o the application

### Description / Background

When the REST API was created the routes were not exposed as instance properties only the base path. Adding the integration to the Python API has mean that the route had to be hard coded and these will get harder to maintain when more routes are added.

See this comment https://github.com/gchq/sleeper/pull/7864#discussion_r3756072501

### Technical Notes / Implementation Details

Save the routes created as instance properties and define a pattern for future routes.

### Dependencies / Blockers

NA

Start by reading the existing REST API route definitions and the instance properties that currently expose only the base path. Review the linked pull-request discussion for context, then define the route properties and confirm that the Python API integration no longer needs hard-coded routes and that the pattern supports future routes.

Written by the indexing model from the issue text.