[Feature]: Add Codeception configuration and some sample tests

[schmidt-travixmedia]

Feature description

It would be very helpful if a Codeception example configuration could be added, as it would be used in a real project. Tests should ideally be executed using a separate database that is reset after the tests. Example: A user registration is tested; then, a login with the newly registered user is tested. After running the tests, database should be reset so that the user does not exist in the database anymore. The "Pimcore Skeleton" GitHub repository already brings a basic Codeception configuration, see https://github.com/pimcore/skeleton/pull/109