Update CHANGELOG.md

[howieleung]

Description

Please add an informative description that covers that changes made by the pull request and link all relevant issues.

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All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

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• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[Copilot]

Pull Request Overview

This PR updates the CHANGELOG to document recent changes in the SDK, including a redesign of automatic function calls and error handling updates.

• Updated the BREAKING CHANGES section to detail the changes in the automatic function calls design.
• Added information regarding the new error format returned by several tool execution methods.
• Included a bug fix note for an infinite loop issue in the Agent create_and_process_run function.

Comments suppressed due to low confidence (1)

sdk/ai/azure-ai-projects/CHANGELOG.md:21

• [nitpick] Consider using a valid JSON format with double quotes (e.g. '{"error": "[message]"}') for improved clarity in describing the error output.

* Because of the function calls redesign, when errors occur in `ToolSet.execute_tool_calls`, `AsyncToolSet.execute_tool_calls`, `FunctionTool.execute` and `AsyncFunctionTool.execute`, they return a JSON string in the format of `{error: [message]}` instead of throwing errors.

[azure-sdk]

API change check

API changes are not detected in this pull request.