[docs] Add performance benchmarking guide and contributor guidelines

[aviralgarg05]

Description

This commit addresses issue #14111 by documenting the investigation into performance change detection tooling for the OpenTelemetry Collector.

Changes:

• Created comprehensive performance-benchmarking.md guide covering:
  • Running benchmarks locally (make gobenchmark, timebenchmark)
  • Writing benchmark tests following Go conventions
  • CodSpeed continuous performance monitoring integration
  • Best practices for performance-sensitive code changes
  • Troubleshooting common benchmark issues
• Updated CONTRIBUTING.md with Performance Testing section
• Added changelog entry documenting the enhancement

The investigation found that CodSpeed (integrated in PR #14160) provides continuous performance regression detection on all PRs and commits to main, with <1% variance and commit-level differential flamegraphs.

This documentation enables contributors to understand the performance testing infrastructure and follow best practices when making changes that could affect collector performance.

Link to tracking issue

Fixes #14111

Testing

NA

Documentation

Created Performance Benchmarking Guide
File: docs/performance-benchmarking.md
Updated CONTRIBUTING.md
File: CONTRIBUTING.md

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: aviralgarg05 / name: Aviral Garg (8021aaa, cf33fe2)

[dmathieu]

Please avoid force-pushing PRs. That breaks the GitHub review UI.

[aviralgarg05]

Please avoid force-pushing PRs. That breaks the GitHub review UI.

Sorry! will keep in mind next time

[codspeed-hq]

CodSpeed Performance Report

Merging #14234 will improve performances by ×2.9

_{Comparing aviralgarg05:docs/add-performance-benchmarking-guide (8021aaa) with main (7012862)}

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

Summary

⚡ 2 improvements
✅ 71 untouched

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	zstdWithConcurrency	19 µs	6.6 µs	×2.9
⚡	BenchmarkSplittingBasedOnItemCountManySmallLogs	3.3 ms	2.4 ms	+35.11%

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.16%. Comparing base (7012862) to head (8021aaa).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14234      +/-   ##
==========================================
- Coverage   92.16%   92.16%   -0.01%     
==========================================
  Files         668      668              
  Lines       41463    41463              
==========================================
- Hits        38216    38214       -2     
- Misses       2214     2215       +1     
- Partials     1033     1034       +1     

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