Adding MariaDB and PerconaDB

MariaDB and Percona (DB) are both forks of the popular MySQL database. They are often used as more performant, open source alternatives to MySQL especially for managed hosting platforms. They’re also sponsored and used by corporate tech companies like Microsoft, IBM, Tencent, Alibaba, RedHat, and others.

- https://mariadb.com
- https://www.percona.com
- https://github.com/percona
- https://github.com/MariaDB/server
- https://docs.acquia.com/acquia-cloud/arch/tech-platform
- https://pantheon.io/blog/using-mariadb-mysql-replacement

Also added reference for Pantheon platform.

Refer to #2670, #2671