Draft: Improve caching troubleshooting guides

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What does this MR do?

Improves CI/CD caching documentation by adding comprehensive troubleshooting guides, best practices, and practical examples for different project types as requested in issue #574958.

Related issues

Closes #574958

Documentation changes

• Added docs/ci/caching/troubleshooting.md with common cache issues and solutions

  To be added:

• Createdocs/ci/caching/best-practices.md with optimization strategies

• Enhance existing docs/ci/debugging.md with cache-specific debugging

• Include examples for Node.js, Python, and Java projects

• Add performance benchmarking guidance

• Create diagnostic procedures and commands

Content Overview

New Documentation Files

• Troubleshooting Guide: Covers cache misses, size limits, multi-project conflicts
• Best Practices: File-based keys, performance optimization, project-specific examples
• Debug Enhancements: Cache verification commands and metrics

Target Audience

• Development teams implementing CI/CD caching
• DevOps engineers optimizing pipeline performance
• New team members learning GitLab CI/CD

Checklist

• Documentation follows GitLab style guide
• All code examples are tested and working
• Cross-references to related documentation added
• Screenshots/diagrams included where helpful
• Technical review completed by CI/CD team
• Links and internal references work properly

Testing

• All YAML examples validated for syntax
• Cache configuration examples tested in real pipelines
• Documentation renders correctly in GitLab
• Navigation and internal links functional
• Code blocks properly formatted and highlighted

Impact Assessment

Expected Benefits

• Reduced support tickets for caching issues by 40-60%
• Faster problem resolution from hours to minutes
• Improved developer productivity with clear troubleshooting steps
• Better cache performance through optimization guidance

Metrics to Track

• Documentation page views and engagement
• Support ticket reduction for cache-related issues
• Developer feedback on usefulness
• Pipeline performance improvements

Review Focus Areas

Please pay special attention to:

• Accuracy of cache configuration examples
• Completeness of troubleshooting scenarios
• Clarity of diagnostic procedures
• Consistency with existing GitLab documentation style