Authentication endpoints coverage

Documentation should be provided for the `/auth` endpoints which are responsible for user authentication in the panel. It is not part of any specific API and is not classed as it's own separate one, so I think it would be best placed under `/pterodactyl/auth`. This should also include information and usage of session tokens.

### Sources
* [routes/auth.php](https://github.com/pterodactyl/panel/blob/b23f3114e4cb71406e6de17d0dca0d88205f56c1/routes/auth.php)
* [app/Http/Requests/Auth](https://github.com/pterodactyl/panel/tree/1.0-develop/app/Http/Requests/Auth)
* [app/Http/Controllers/Auth](https://github.com/pterodactyl/panel/tree/b23f3114e4cb71406e6de17d0dca0d88205f56c1/app/Http/Controllers/Auth)

Start with routes/auth.php, then review app/Http/Requests/Auth and app/Http/Controllers/Auth to identify the authentication endpoints and their request handling. Add documentation under /pterodactyl/auth covering each endpoint and session-token usage; the work is done when the /auth coverage is complete and the documented behavior matches those sources.

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