fix(mariadb): drop MySQL-only and deprecated options from the chart's my.cnf #4842

The MariaDB chart's my.cnf carries options that every shipped server version either ignores or warns about. This only became visible once the file is actually read again (#4836). Until then the server never loaded it.

I rendered packages/apps/mariadb/templates/config.yaml with the defaults and started each image from files/versions.yaml with it in /etc/mysql/conf.d. All four start fine. These are the warnings they log:

# 10.6.24, 10.11.15, 11.4.9, 11.8.5
[Warning] 'default-authentication-plugin' is MySQL 5.6 / 5.7 compatible option. To be implemented in later versions.
[Warning] 'master-info-repository' is MySQL 5.6 / 5.7 compatible option. Not used or needed in MariaDB.
[Warning] 'relay-log-info-repository' is MySQL 5.6 / 5.7 compatible option. Not used or needed in MariaDB.

# 11.8.5 only
[Warning] --innodb-flush-method is deprecated and will be removed in a future release

The first three are MySQL options and do nothing on MariaDB, so they can just go. The flush method one matters more. When a future MariaDB release removes the option, an unknown variable in my.cnf stops the server from starting, so the chart would break on the version bump. MariaDB's replacement is a set of separate innodb_* switches. Mapping O_DIRECT_NO_FSYNC onto them needs checking against each shipped version, because the chart still ships 10.6.