Use sessions instead of API keys for admin authentication

[Frewacom]

Using API keys for authentication is probably not our best option. It comes with a bunch of security implications and is harder to correctly and securely implement compared to sessions. Luckily, since we are using Adonis, this change is really simple to do. Tests will be a PITA, though.

[McFrappe]

https://docs.adonisjs.com/guides/session#session-id-lifecycle

Cant wait to update all the tests so that they conform to session based. 🥲

Oh well, I'm doing this for my future self etc.