Change rails server command for preflight checks

From draft to ready

• Remove the two cherry-picked commits from !119135 (commits)
• Remove another test commit (!119502 (2a9ee99b))

Context

In gitlab-org/quality/engineering-productivity/review-apps-broken-incidents#94 (closed), we noticed that a pipeline had a successful preflight check, but failed to deploy review-apps because of a Puma error (see RCA).

What does this MR do and why?

• Change the rails server command in the preflight check to use the same command that is used in the CNG project.
• Adapt the command to run with a puma.rb file coming from config/puma.rb.example in the repo.
  • This might not be the exact same config as the config we use in the CNG project, but it is one that is available from gitlab-org/gitlab and that is hopefully regularly updated.

Does it work?

I added a commit (!119502 (2a9ee99b)) that introduce the same error as seen in the incident (gitlab-org/quality/engineering-productivity/review-apps-broken-incidents#94 (comment 1373249719)). I also added the content of the original MR to upgrade Puma to version 6.x.

The preflight job detected that error 🎉 : https://gitlab.com/gitlab-org/gitlab/-/jobs/4258796235

MR acceptance checklist

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

• I have evaluated the MR acceptance checklist for this MR.