Fix MariaDB data removal
requested to merge lvoytek/mysql:mysql-8.0/lena/fix-mariadb-data-removal into mysql-8.0/debian/latest
Finally working to resolve #853008 by adding checks for MariaDB on install and removal.
When installing mysql-server, the preinst matches mariadb-server's behavior by checking for a debian-*.flag file to check if MariaDB exists. If so, it moves the data to a new location in the same way, and shows the info in the attached image.
When removing mysql-server-8.0, the postrm checks again for MariaDB in the same way. If it is detected it notifies the user. On a purge the files are not removed when MariaDB is detected.