feat: Frontend - Create User signup page

[junocchi]

Acceptance criteria

As a new user, I want to be able to create an account with Aura. Once the logic (part of the ticket #16) is done, the users should be able to create a new account with a Username, E-mail address and password

[pablisch]

We discussed using Google accounts for signup which would work well for this. We did talk about also allowing email signup but I wonder if we should consider Google as the primary signup/login functionality. Obviously, this is a backend thing but it very much affects the page too.