[IMPROVEMENT] Authentication GraphQL mutation

[YummYume]

Type of feature

An improvement to something that already exists

The name of the feature

Improve the authentication endpoint

Feature description

Authentication should be done from a non-mapped resource called Token.

• Create a non-mapped resource called Token.
• Move the mutation for login to this new resource.
• Migrate the token and tokenTtl properties from the User to this new resource.
• Login should now be called request (for requestToken).

Additional information

Linked to #37.