Implement account creation & account deletion UX

[dzenbot]

The API endpoint user/register now works reliably (still in dev), and a new API endpoint user/register has been added. With these 2 methods we can now implement a native UX to create an account and delete it, while complying with Apple's account deletion requirements.

TODO:

• Map both endpoints in RaceSyncAPI
• Show new form view to create an account, launch from the login view.
• Handle all the known form errors (ie: Existing email, existing username, etc)
• Implement a non-obstructing alert to notify the user that an email was sent to them, and return to login view
• Show 'Delete Account' option from within the app settings. A destructive action sheet should be presented, before proceeding.
• Handle navigation flow after deleting an account, by logging out and showing the login view