Move code coverage examples to the documentation

The coverage regex examples in the CI / CD Settings page (e.g. https://gitlab.com/gitlab-org/gitlab-ce/settings/ci_cd) should be moved to the documentation page: https://gitlab.com/help/user/project/pipelines/settings#test-coverage-parsing

Based on https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/14199#note_41475485 and https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/14199#note_43832050.