Add glab in release-cli docker image
What does this MR do and why?
We are adding the glab executable in the release-cli image so that all new release-cli:latest image fetch will include glab (#194 (closed)).
This will help our long-term goal of migrating from release-cli to glab (&15437 (closed)).
Also, we will be able to continue working on gitlab#442785 (closed).
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