Make ChatClient and Advisor APIs more robust - Part 2

[ThomasVitale]

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• ChatClient observations now include the full prompt content instead of just the userText and systemText. Furthermore, they include consistent telemetry for the tools passed via the ChatClient and a first-class conversation ID when using memory advisors. Incomplete or unsafe attributes have been deprecated.
• Adopted the new robust Advisor APIs for BaseAdvisor and RetrievalAugmentationAdvisor.
• Improved the prompt augmentation facilities in ChatClientRequest and Prompt for performance and immutability.
• Fixed integration test racing condition.
• Updated the documentation for ChatClient and Observability accordingly.
• Documented changes in upgrade notes.

Relates to gh-2655