Configure behat in the build stage so that the config file is part of the artifacts and doesn't get reset by parallel test processes

Add the steps to the build theme job, projects using this should chdir into the correct directory by using the before_script directive

Enable build and theme tasks even if CI tests are disabled, because we require theme artefacts for deployment

Implement an optional variable $DISABLE_CI_TESTS which prevents the stages build, prepare and test when set

Do not execute any of those tasks if variable $CAE is provided because that should then only trigger config collection

Define variable GIT_STRATEGY on a per task basis to avoid influencing other tasks that might be included by the parent too