Draft: Add a way to skip as-if-jh jobs

What does this MR do and why?

Add a way to skip as-if-jh jobs, if ~"pipeline:skip-as-if-jh" is presented, skip them.

This provides a way to reduce the number of jobs for merge requests already having a lot of jobs, and we want to speed it up somehow.

An example is !83921 (comment 896499555) where it had 712 jobs, which was quite a lot! Skipping as-if-jh jobs can reduce it to 605, which was still a lot but it did help.

How to set up and validate locally

I added both pipeline:run-as-if-jh and ~"pipeline:skip-as-if-jh" and I expect there are no as-if-jh jobs.

MR acceptance checklist

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