Add gitlab-housekeper CI template to run in CI

What does this MR do and why?

Per the instructions in https://gitlab.com/gitlab-org/gitlab/-/tree/master/gems?ref_type=heads#development-guidelines we need to ensure all gems in gems/ directory have a corresponding entry in .gitlab/ci/gitlab-gems.gitlab-ci.yml to run their rspec jobs in CI.

This was missed in !139492 (merged) .

MR acceptance checklist

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.