Fix mysql native authentication for 8.4

[daniel-memo-ict]

In #185 you've made some changes to always use mysql 8.0, because there was a problem in 8.4 with mysql_native_authentication

However when upgrading to the newer mysql, if we've already been using an image made with mysql 8.1, 8.2 or 8.3, we'll be forced to throw away our databases as we cannot downgrade to 8.0

A better fix for mysql 8.4 would be to enable mysql_native_authentication again. This plugin was still enabled in 8.3, but was disabled in 8.4.

To enable mysql_native_authentication again, you could add an extra line to your mysql.cnf.

The server-side plugin is built into the server, but is disabled by default. To enable it, start the MySQL Server with --mysql-native-password=ON or by including mysql_native_password=ON in the [mysqld] section of your MySQL configuration file.