Clean up the old Azure Functions examples

[zhenlan]

• Relevant Azure Functions documents have been updated with the new examples. This is the last step to clean up old examples. https://github.com/Azure/AppConfiguration/tree/main/examples/DotNetCore/AzureFunctions
• Updated examples to take CancellationToken for async feature evaluation, showcasing a new feature added in the latest feature management release.

[Copilot]

Pull Request Overview

This pull request cleans up outdated Azure Functions examples by removing deprecated example files and updating the remaining ones to demonstrate the new async feature evaluation with CancellationToken support. Key changes include:

• Updating the examples to pass CancellationToken (req.HttpContext.RequestAborted) to async feature evaluations.
• Removing all legacy Azure Functions examples (in-process, out-of-process, etc.) that are no longer maintained.
• Revising the README file to reflect the new examples and updated folder structure.

Reviewed Changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated no comments.

File	Description
examples/README.md	Updated headings, links, and descriptions for new examples.
examples/DotNetCore/AzureFunctions/FunctionAppIsolated/ShowBetaFeature.cs	Updated IsEnabledAsync call to include CancellationToken.
examples/DotNetCore/AzureFunctions/FunctionAppInProcess/ShowBetaFeature.cs	Updated IsEnabledAsync call to include CancellationToken.
Other files in examples/DotNetCore/AzureFunction/*	Entirely removed legacy Azure Functions examples.

Comments suppressed due to low confidence (2)

examples/README.md:5

• [nitpick] Verify that the folder naming convention ('AzureFunctions' vs. 'AzureFunction') is consistent across the documentation and project directories to avoid potential confusion.

### [Azure Functions (Isolated worker model)](./DotNetCore/AzureFunctions/FunctionAppIsolated)

examples/README.md:9

• [nitpick] Ensure that the naming and descriptions for the in-process example are aligned with the updated structure and clearly distinguish between isolated and in-process models.

### [Azure Functions (In-process model)](./DotNetCore/AzureFunctions/FunctionAppInProcess)