Use php-base image for drush and other tooling

The following discussion from !1 (merged) should be addressed:

• @kosamara started a discussion: (+3 comments)

  If we stick to the latest discussions in https://gitlab.cern.ch/webservices/webframeworks-planning/-/issues/244 , this image will go and instead drush can be installed in php-base (and therefore composer). We should also install a mysql client there.