Optimize kubernetes_variables calculation
## Summary
Using [the steps defined in the main Epic](https://gitlab.com/groups/gitlab-org/-/epics/7290#note_828760836), I downloaded the `stackprof` profile report and used it in `https://www.speedscope.app/` to see the slowest part of the pipeline creation.
This looked interesting;
We are spending 1.25 seconds to calculate `kubernetes_variables`.
issue
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