Updating dotnet samples to NET 9

[PabloNunes]

The current samples in the repository are using older versions of .NET. With .NET 9 now available, it would be beneficial to update the samples to demonstrate modern best practices and take advantage of new features.

Suggested updates:

• Upgrade or make NET 9 samples, focusing on using console Apps as new medium
• Update documentation to reflect the changes

Projects to be Updated:

• [ ] 06 - Text Generation Apps
• [ ] 07 - Building Chat Applications
• [ ] 08 - Building Search Applications
• [ ] 09 - Building Image Applications

Projects to be made:

• [ ] 04 - Prompt Engineering Fundamentals
• [ ] 05 - Creating Advanced prompts
• [ ] 11 - Integrating with function calling
• [ ] 15 - Retrieval Augmented Generation (RAG) and Vector Databases
• [ ] 18 - Fine-Tuning Your LLM
• [ ] 19 - SLM
• [ ] 20 - Mistral
• [ ] 21 - Meta

Pinging: @codemillmatt, @elbruno

[github-actions[bot]]

👋 Thanks for contributing @PabloNunes! We will review the issue and get back to you soon.

[codemillmatt]

@koreyspace - I'd like to either keep this issue open or create new ones for each sample that needs updating please.

The .NET samples here are pretty old and are not showing best practices (or tbh - I'm not even sure they work).

I'll wait for your guidance on how you'd like to proceed.