[18.7] Patch io-event gem to drop epoll_pwait2 check for RedHat 9

What does this MR do and why?

This backports !9193 (merged) to 18-7-stable.

Some distributions (e.g. RedHat 9.7) ship glibc 2.34 with backported epoll_pwait2 support tagged as GLIBC_2.35, causing binaries built there to fail on systems with a true glibc 2.34 (RedHat 9.6).

This change:

• Adds a new ruby-io-event software definition that rebuilds the io-event gem without the epoll_pwait2 check on RedHat 9 systems.
• Adds the ruby-io-event dependency to the gitlab project for RedHat 9.
• Adds a el_9? helper method to OhaiHelper for platform detection

https://github.com/socketry/io-event/pull/159 would avoid the need for this patching.

Relates to https://gitlab.com/gitlab-com/request-for-help/-/work_items/4332

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The original MR has been deployed to GitLab.com (not applicable for documentation or spec changes).
• This MR has a severity label assigned (if applicable).

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