Make version of PHP image dynamic

Currently we have the image for PHP hard coded in the GitLab runner config file.

We can easily add image overwrites to each task in the pipeline by using the PHP_VERSION variable to utilize the PHP version already configured for each Drupal project danymically.

added To Do label

added Doing label and removed To Do label

assigned to @jurgenhaas

mentioned in commit 25d5c191

mentioned in commit eeaa9a77

A variable value can only contain strings or number, but not 7.4 so we had to break it up into 2 variables:

  PHP_MAJOR_VERSION: 7
  PHP_MINOR_VERSION: 4

This is now implemented with these default values and can be overwritten by the including project.

closed

removed Doing label