feat(core): allow clearing cookies from `jwt()` (#6337)
* feat(core): allow clearing cookies from `jwt()`
* revert: allow clearing cookies from `jwt()`
* feat(core): re-apply changes against `@auth/core`
* revert: `decodeJWT` option
* doc: `jwt()` callback
* Apply suggestions from code review
Co-authored-by: Balázs Orbán <info@balazsorban.com>
