[SPIKE] Investigate Kibana logs for ref_exists_in_gitaly? fallback

Context

In version %18.0, we introduced Pull ref from Gitaly if not present in Redis (!188492 - merged), which serves as a fallback when the Redis cache is stale and the reference exists in Gitaly. As of today, we have 3,452 discrepancies between the Redis cache and Gitaly.

Expectations

• Investigate these cases and track the different services using the correlation ID in Kibana.
• Try to identify a common pattern or potential causes by reviewing the logs.
• Try to solve the following questions: Why are we using the fallback? What makes these requests different?
• If a common pattern or root cause is not found. What information are we missing? Do we need to add more logging?

References

• [Feature flag] Rollout of `pull_ref_directly_fr... (#536824 - closed)
• #536824 (comment 2507976887)
• #536824 (comment 2512117608)