Improve Contributor Guide

[RichardChukwu]

part of open-telemetry/sig-contributor-experience#31

Changes

This PR enhances the CONTRIBUTING.md file by improving its structure, clarifying build prerequisites, and addressing common build issues. The goal is to make it easier for first-time contributors to get started with opentelemetry-cpp.

Key Change:

✅ Added a Prerequisites Section

• Listed required tools with version recommendations, including C++ compilers, CMake, Bazel, clang-format, and markdownlint-cli.
• Specified Bazel 7.1.1 as the recommended version for building examples.

Why These Changes?

The previous version lacked explicit versioning details for Bazel, leading to build errors.
The new structure provides a clearer path for first-time contributors.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes

[netlify]

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Name	Link
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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.96%. Comparing base (821ad9e) to head (21e416e).

Additional details and impacted files

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##             main    #3264   +/-   ##
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  Coverage   87.96%   87.96%           
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  Files         205      205           
  Lines        6407     6407           
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  Hits         5635     5635           
  Misses        772      772