Resolve documentation discrepancies between Flaky Tests SSOT, Quarantine Process SSOT, automated flaky test issues, and unhealthy tests docs

Problem Statement

We have many sources of information about flaky tests and quarantining that contain discrepancies and violate SSOT principles:

1. Flaky Tests SSOT
2. Quarantine Process SSOT
3. Automated flaky test file issues (generated by ci-alerts)
4. 🆕 https://docs.gitlab.com/development/testing_guide/unhealthy_tests/ 🆕

Goal

Ensure each documentation source has a clear, single responsibility and cross-references appropriately:

• Flaky Tests SSOT: Only covers flaky test identification, detection, and troubleshooting
• Quarantine Process SSOT: Only covers quarantining processes and procedures
• Automated issues: Link to both SSOTs appropriately