Draft: Set ENABLE_PUMA_NAKAYOSHI_FORK to true by default

What does this Merge Request do?

⚠ Please don't merge yet. Needs sync with other related MRs, please check gitlab-com/gl-infra/k8s-workloads/gitlab-com!652 (comment 494329652)

Enables nakayoshi_fork for Puma.

Because the related incident was resolved (gitlab-com/gl-infra/production#3370 (closed)) and the source of the issue was patched (gitlab!52177 (merged)), and we also established a single name for the env variable(!1775 (diffs), gitlab-org/build/CNG!587 (diffs), omnibus-gitlab!4941 (diffs)), we are ready to set ENABLE_PUMA_NAKAYOSHI_FORK: "true" by default.

See: gitlab#288042 (comment 494061932)

Related:

• gitlab-com/gl-infra/k8s-workloads/gitlab-com!652 (merged)
• gitlab-org/charts/gitlab!1795 (closed)
• omnibus-gitlab!4964 (closed)

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.