Add Observability section to CONTRIBUTING doc

[MrAlias]

Adds an Observability section to the CONTRIBUTING.md documentation. This is a follow-up to issue #2547 (comment) and provides guidance for implementing self-observability in OpenTelemetry Go SDK components.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.9%. Comparing base (4107421) to head (6dd354e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #7272   +/-   ##
=====================================
  Coverage   82.9%   82.9%           
=====================================
  Files        265     265           
  Lines      24894   24894           
=====================================
+ Hits       20641   20643    +2     
+ Misses      3878    3876    -2     
  Partials     375     375           

see 2 files with indirect coverage changes

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[Copilot]

Pull Request Overview

This PR adds a comprehensive "Observability" section to the CONTRIBUTING.md documentation, providing detailed guidance for implementing self-observability in OpenTelemetry Go SDK components. This addresses issue #2547 by establishing best practices for instrumenting SDK components themselves.

Key changes:

• Adds extensive documentation on self-observability patterns and best practices
• Provides code examples for proper instrumentation setup, performance optimization, and testing
• Establishes guidelines for semantic conventions compliance and error handling

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[dashpole]

I love this. Can we incorporate any of this advice into our docs in opentelemetry.io?