Endpoint to support add accept command

## Proposed endpoint

Add the necessary get/put endpoints to support feature request #18 in the cli. This would be from the **students perspective** not the instructors. Currently all commands in the classroom cli return information using the instructors token.

For this to work for a student, this endpoint would need to return all the classrooms and assignments that a **student** can access with their own auth token.

## Justification

This will be used to implement #18 and make classrooms usable without a student having to use a browser. Lots of schools provide ssh access to local clusters that don't support x11 forwarding so we need tools that are 100% cli to help foster adoption :)

Inizia leggendo la richiesta di funzionalità #18 e tracciando i comandi CLI di classroom esistenti che usano un token dell’istruttore. Identifica gli endpoint attuali di classroom e assignment, quindi definisci il comportamento GET/PUT autenticato dallo studente e verifica che gli studenti possano accedere solo alle classrooms e agli assignments disponibili per loro.

Scritto dal modello di indicizzazione a partire dal testo della issue.