Allow gitlab ci to be detected

[BackEndTea]

Gitlab CI wasn't being detected by the CiDetectedErrorFormatter. This MR allows detection so that the CiDetectedErrorFormatter can be used for gitlab as well.

[ondrejmirtes]

AFAIK GitLab still only shows these results in paid tiers: https://docs.gitlab.com/ee/ci/testing/code_quality.html

That's why GitLab CI is not currently detected by default. Maybe it's part of GITLAB_FEATURES env variable, I'm not sure. If you research that and detect correctly then I'd merge that.