Eager load production app in CI

Context

Follow-up of https://gitlab.com/gitlab-org/quality/engineering-productivity-infrastructure/-/issues/77#tasks

From Draft to Ready

• Remove all of the blocking questions I have in the MR.

What does this MR do?

Add a job that loads the production application. It's an early-fail mechanism to detect missing gems, configuration errors, ...

Does it work?

• The job passed for a "regular MR" (2e1111c8): https://gitlab.com/gitlab-org/gitlab/-/jobs/3734181134
• The job failed for an MR where we reintroduced a require 'byebug' 🎉 (d59f9b5d): https://gitlab.com/gitlab-org/gitlab/-/jobs/3734215559

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.