Updating first quickstart to reflect new sample separation of OpenAI and Azure OpenAI

[jmatthiesen]

Summary

We're simplifying the SDKs used in our AI quickstarts to focus on using Semantic Kernel, and demonstrating how to use either OpenAI or Azure OpenAI as the host service. These updates accompany a samples update tracked in the following PR:

dotnet/ai-samples#71

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Internal previews

📄 File	🔗 Preview link
docs/ai/quickstarts/get-started-azure-openai.md	CustomerIntent: As a .NET developer new to AI, I want deploy and use sample code to interact to learn from the sample code.
docs/ai/quickstarts/quickstart-ai-chat-with-data.md	Get insight about your data from an .NET Azure AI chat app
docs/ai/quickstarts/quickstart-azure-openai-tool.md	Extend Azure AI using Tools and execute a local Function with .NET
docs/ai/quickstarts/quickstart-openai-generate-images.md	Quickstart - Generate images using Azure AI with .NET
docs/ai/quickstarts/quickstart-openai-summarize-text.md	CustomerIntent: As a .NET developer new to Azure OpenAI, I want deploy and use sample code to interact to learn from the sample code to summarize text.