feat: Password-less login with WebAuthn

[jay-dee7]

Instead of one large interface to cover for everything, we now have
multiple, smaller interfaces to make our backend more composable.
Refactor goes like this:

// Postgres Core
type PgTxnHandler interface {
    NewTxn(ctx context.Context) (pgx.Tx, error)
    Abort(ctx context.Context, txn pgx.Tx) error
    Commit(ctx context.Context, txn pgx.Tx) error
}

// User specific
type UserReader interface  {
    PgTxnHandler
    ...
}
type UserWriter interface  {
    PgTxnHandler
    ...
}
type UserDeleter interface  {
    PgTxnHandler
    ...
}
type UserReadWriteDeleter interface  {
    PgTxnHandler
    ...
}

// WebAuthn specific
type WebAuthn interface {
    PgTxnHandler
    UserReader
    UserWriter

    GetWebAuthNSessionData(ctx context.Context, userId string, sessionType string) (*webauthn.SessionData, error)
    AddWebAuthSessionData(ctx context.Context, userId string, sessionData *webauthn.SessionData, sessionType string) error
    GetWebAuthNCredentials(ctx context.Context, userId string) (*webauthn.Credential, error)
    AddWebAuthNCredentials(ctx context.Context, userId string, credential *webauthn.Credential) error
}

[guacamole]

Awesome work @jay-dee7 🥇 💯