Re-add DiffBlue CI template after broken master
What does this MR do and why?
This MR is to re-add the DiffBlue-Cover.gitlab-ci.yml
template since the original attempt to add it broke master.
Original MR: !137047 (merged)
Failing specs that broke master: https://gitlab.com/gitlab-org/gitlab/-/pipelines/1092132905/failures
Revert MR: !138492 (merged)
MR acceptance checklist
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