Enable `nakayoshi_fork` for Puma by default

What does this Merge Request 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.

Related MRs

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

Merge Request checklist

• [-] Tests added for new functionality. If not, please raise Issue to follow-up.
• This change is backward compatible. If not, please include steps to communicate to our users.
• [-] Documentation added/updated, if needed.
• [-] gdk doctor test added, if needed.