Move code coverage examples to the documentation

The coverage regex examples in the CI / CD Settings page https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/views/projects/settings/ci_cd/_form.html.haml#L113 should be moved to the documentation page: https://docs.gitlab.com/ee/ci/pipelines/settings.html#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.