Add deprecation guide for packages and APIs

[Copilot]

Description

Adds comprehensive deprecation documentation at /doc/deprecation.md covering package and API lifecycle management.

Changes

• Created /doc/deprecation.md

  • Links to Azure SDK support/deprecation policies (no content duplication)
  • C++ implementation patterns using [[deprecated]] attributes
  • Doxygen @deprecated documentation conventions
  • Package-level deprecation workflow
  • Migration guide requirements and examples

• Updated README.md and CONTRIBUTING.md

  • Added navigation links to deprecation guide

Example Usage

/**
 * @brief Performs an old operation.
 * 
 * @deprecated This function is deprecated as of version 2.0.0.
 * Use NewFunction() instead for improved performance.
 */
[[deprecated("Use NewFunction() instead. Removed in version 3.0.0.")]]
int OldFunction(int input);

Pull Request Checklist

• C++ Guidelines
• Doxygen docs
• Unit tests - N/A (documentation only)
• No unwanted commits/changes
• Descriptive title/description
  • PR is single purpose
  • Related issue listed
• Comments in source - N/A (documentation only)
• No typos
• Update changelog - N/A (documentation only)
• Not work-in-progress
• External references or docs updated
• Self review of PR done
• Any breaking changes? - No

Warning

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• azure.github.io
  • Triggering command: /usr/bin/curl curl -s REDACTED (dns block)
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node /home/REDACTED/work/_temp/ghcca-node/node/bin/node --enable-source-maps /home/REDACTED/work/_temp/copilot-developer-action-main/dist/index.js (dns block)

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Original prompt

---

This section details on the original issue you should resolve

<issue_title>Add document describing how to deprecate packages</issue_title>
<issue_description>Add instructions on how to deprecate modules into a document at /doc/deprecation.md (or similar).
Link the page in our repo to the Azure SDK "Deprecating Azure SDKs" page.

General SDK patterns for deprecation should be followed.

Do not duplicate information that is already in the https://azure.github.io/azure-sdk/policies_support.html document. Link to the relevant sections.
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add document describing how to deprecate packages #5705

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