Properly support disabling rack-timeout logging

What does this MR do and why?

This MR fixes !90958 (merged) by properly supporting the ability to disable rack-timeout logging. I discovered the Gitlab::Runtime.puma? was not firing when running Rails like gdk rails server, so the ENV['GITLAB_RAILS_RACK_TIMEOUT_ENABLE'] check needs to exist outside of the existing logic and at the end.

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