Document configuration decisions

Add explanatory comments to configuration files that clarify the reasoning behind non-obvious choices, feature exclusions, conditional logic, and environment-specific settings. This helps future maintainers understand why certain configurations exist and prevents accidental modifications.

Key areas requiring documentation:

• Feature flags and their exclusions/inclusions
• Conditional logic in workflows or config files
• Environment-specific behavior
• Default values that may not be immediately obvious

Example:

env:
  # Driver adapters are a special feature, 
  # so in our "normal" tests, we don't enable it yet to keep things separated, 
  # also because they are tested in a separate job.
  EXCLUDED_PREVIEW_FEATURES: 'driverAdapters'
  
  # Exclude relationJoins tests with WASM because the WASM engine does not include the necessary changes yet.
  EXCLUDED_PREVIEW_FEATURES: $

This practice prevents confusion about configuration intent and reduces the likelihood of breaking changes when configurations are modified.