Enable `nakayoshi_fork` by default

What does this MR do?

nakayoshi_fork was enabled on production already for some time, and we didn't see any issues with GC.compact and in general.

We consider having it enabled by default.

We don't plan to expose the config to our users, as we expect it to be always beneficial, and we observed it being enabled on production long enough without causing any issues with GC.compact.

We will still keep the ENV variable for .com, so it would be easier to disable it in case of any misbehavior.

This is the rework of !4964 (closed)

Related MRs

• GitLab: gitlab!54688 (merged)
• Omnibus: !5022 (merged)
• CNG: gitlab-org/build/CNG!599 (merged)
• GDK: gitlab-development-kit!1832 (merged)

Checklist

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• Merge Request Title, and Description are up to date, accurate, and descriptive
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