As you can see inside the docs, ASConfig.php file is being created after successful installation. So, once you install the latest version of the app, the ASConfig.php file will be created.
The error you are getting during the installation process has nothing to do with MySQL version. I've fully tested the app on MySQL 5.7, and haven't found any issues. According to the error message, it looks like your credentials are incorrect.
Are you sure that the username for your database user is correct? Also, are you able to connect to the DB from some other application?