FF rollout truncate commit message in CI env var

Issue:

• [FF] `truncate_ci_commit_message` -- Truncate l... (#576807 - closed) • Ashvin Sharma • 18.6
• Kubernetes Runner - large commit messages cause... (gitlab-runner#26624 - closed) • Ashvin Sharma • 18.6

What does this MR do and why?

FF rollout truncate commit message in CI env var

This was behind a feature flag in !208666 (merged).

Large commit messages (100 KiB by default) will be truncated when sent to Job runner to avoid job failures.

References

Introduced in MR: Truncate commit message if it breaches size limit (!208666 - merged) • Ashvin Sharma • 18.6

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