feat(coverage): implement automated coverage validation tool (#14098)

[sAchin-680]

Description

This PR implements automated code coverage validation for OpenTelemetry Collector components as outlined in issue #14098. The new checkcover tool enforces coverage requirements based on component stability levels and integrates seamlessly into the existing CI pipeline.

Key Features:

• Enforces 80% minimum coverage for stable components
• Supports repository-wide minimum via CLI flag (--repo-minimum)
• Allows components to set higher requirements via coverage_minimum in metadata.yaml
• Integrated into CI workflow (runs after test-coverage job)
• Includes comprehensive unit tests and documentation

Link to tracking issue

Addresses #14066 (Automate validation and fulfillment of criteria outlined in the "Component Stability" document)

Fixes #14098 (Validate and enforce test coverage requirements)

Testing

• Added unit tests for checkcover tool (validator_test.go)
  • Coverage file parsing and calculation
  • Minimum coverage determination logic
  • Module path resolution
• All tests passing: 8 test cases across 4 test functions
• Verified mdatagen tests still pass with schema changes
• Tool builds successfully and CLI interface works correctly

Documentation

• Tool Documentation: cmd/checkcover/README.md - Usage guide and examples
• User Guide: docs/coverage-requirements.md - Component author guidelines
• Implementation Details: COVERAGE_VALIDATION_IMPLEMENTATION.md - Technical documentation
• Schema Documentation: Updated cmd/mdatagen/metadata-schema.yaml with coverage_minimum field description
• All documentation includes examples and troubleshooting guidance

[codecov]

Codecov Report

❌ Patch coverage is 27.69953% with 154 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.91%. Comparing base (09a2719) to head (cf8161f).

Files with missing lines	Patch %	Lines
cmd/checkcover/validator.go	32.57%	109 Missing and 9 partials ⚠️
cmd/checkcover/main.go	0.00%	32 Missing ⚠️
cmd/mdatagen/internal/status.go	33.33%	2 Missing and 2 partials ⚠️

❌ Your patch check has failed because the patch coverage (27.69%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14134      +/-   ##
==========================================
- Coverage   92.24%   91.91%   -0.34%     
==========================================
  Files         657      659       +2     
  Lines       41068    41281     +213     
==========================================
+ Hits        37884    37944      +60     
- Misses       2179     2321     +142     
- Partials     1005     1016      +11     

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[dmathieu]

From a quick look:

IMHO, the command would be better off in internal/cmd. This is not needed as a public tool.
Also, your PR currently has the compiled binary committed. That should be gitignored.

[sAchin-680]

Thanks @dmathieu! Both fixed in 8a7394e:

• Moved to checkcover (not a public tool)
• Removed binary and added to .gitignore

All tests passing. Let me know if you'd like any further changes or modifications.