Add draft release notes for version 0.5.0

[cleemullins]

Draft release notes for the 0.5.0 release. See comment thread for an easy cut/paste of the notes.

[Copilot]

Pull Request Overview

This PR introduces draft release notes for version 0.5.0 of the Microsoft 365 Agents SDK for Python, documenting major updates including expanded Python version support (3.10-3.14), new sub-channel identification features, comprehensive library documentation, and various developer experience improvements.

Key Changes:

• Documents breaking changes including dropped Python 3.9 support and minimum requirement of Python 3.10
• Highlights new features such as sub-channel identification support and expanded Python version compatibility
• Details developer experience improvements including comprehensive README documentation for all 8 core libraries

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[Copilot]

Pull Request Overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[Copilot]

Pull Request Overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}