Update test images to MySQL 8.4 using the new mysql-native-password flag

[rdimaio]

As part of this issue: #6747

We're pinning MySQL to 8.3 for ftsdb and the mysql8-based images.

In order to support MySQL 8.4, we need to substitute the deprecated --default-authentication-plugin=mysql_native_password flag with the new --mysql-native-password=ON server option, as outlined here: #6747 (comment)

I tried doing it for the mysql8-based images here: rdimaio@326fb8f, but it failed with these logs: #6747 (comment).

Opening this issue to track this work, which is not urgent at the moment (this issue is definitely more important: #6755)