refactor: add isAnonymous property to auth state

[Schwehn42]

Description

This PR adds a new property isAnonymous to the Auth state. This is required by #4201 to differentiate between users that registered anonymously or using one of the providers (Google, Apple, etc).
The reason I didn't just add accountType to the Auth interface is that I think it's easier to handle a boolean than a string, anticipating that this might be used at more than one place.

Changelog

• types/auth.ts:
  • Add isAnonymous prop to Auth interface
  • Add new interface AuthDto resembling the actual json retrieved from backend, which was omitted until now.
• api/auth.ts
  • getCurrentUser(): Cast as AuthDto, as this includes the accountType property
• middleware/auth.tsx
  • set isAnonymous to whether the account is anonymous
• Add isAnonymous prop to other files depending on Auth interface, like getTestApplicationState

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas

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commit sha: 9c915da