This patch updates the PHP images to use the Debian bullseye base image which improves ARM support. At least for PHP 7.3 and newer. PHP 7.2 and lower is still built on top of Debian stretch or buster which likely has no ARM support for everything we need.
It also pins the MySQL 5.7 container on the amd64 platform as it does not support ARM yet.
This patch updates the PHP images to use the Debian bullseye base image which improves ARM support. At least for PHP 7.3 and newer. PHP 7.2 and lower is still built on top of Debian stretch or buster which likely has no ARM support for everything we need.
It also pins the MySQL 5.7 container on the amd64 platform as it does not support ARM yet.
Helps addressing #231 and #230.