Fix linking CreatedSession to Examiner

[henrygoodman]

An examiner can create a CreatedSession (with the generated code), but we need to determine the lifetime of this code

Should it:

• Persist if examiner logs out
• Persist if examiner reloads page (obvious yes)
• Persist if examiner shuts browser
• Persist if examiner accesses from different browser
• Only ever 'end' once the examiner clicks the End Session button.

If so, then an examiner will always have either 0 or 1 createdSessions active at a time, and we should query the DB for that specific session upon login (using NextJS session maybe, as this stores the users name and email which we can use to get an examiner ID, and then a createdSession which is maked as valid)

[henrygoodman]

This might be fine to leave as out-of-scope, there is more important functionality to consider