gitlab-ci: add test report exporting for Gitlab UI

What does this MR do?

It adds integration into Gitlab for the test report generated by Codeception.

More information on what this gives us: https://docs.gitlab.com/ee/ci/unit_test_reports.html

How confident are you it won't break things if deployed?

no chance, worst case it could break testing (which will be obvious on this MR :)

Links to related issues

How to test

Look at the test summary on this MR

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• set a "for:" label to indicate who will be affected by this change
• use "state:" labels to track this MR's state until it was beta tested
• added an entry to CHANGELOG.md
• add a short text that can be used in the release notes
• Once your MR has been merged, you are responsible to create a testing issue in Beta Testing Repo:
  • Consider writing a detailed description in German.
  • Describe in a few sentences, what should be tested from a user perspective.
  • Also mention different settings (e.g. different browsers, roles, ...). how this change can be tested.
  • Be aware, that also non technical people should understand.

Release notes text

(A short text that will appear in the release notes and describes the change for non-technical people. Not always necessary, e.g. not for refactoring.)