.Net: Add Provider Support to ONNX Connector (+CUDA Sample)

[loicbtd]

Motivation and Context

1. Why is this change required?
   Currently, users can configure ONNX execution providers by manually creating a genai_config.json file next to the ONNX model.

2. What problem does it solve?
   This change eliminates the need for manual JSON configuration files by providing a programmatic API for provider configuration, making it easier for developers to configure ONNX execution providers directly through code with the extension methods.

3. What scenario does it contribute to?
   This improves the developer experience when working with ONNX models in Semantic Kernel, particularly for scenarios where:

   • Developers want to dynamically select providers based on runtime conditions
   • Teams prefer code-based configuration over file-based configuration

4. If it fixes an open issue, please link to the issue here.
   Closes .Net: Add Provider Choice Support to ONNX Connector #12828

Description

Changes Made:

• New Provider Class: Added Provider class to encapsulate provider configuration with Id and Options properties
• Enhanced Chat Completion Service: Extended OnnxRuntimeGenAIChatCompletionService to accept the providers parameter.
• Updated Builder Extension: Modified OnnxKernelBuilderExtensions.AddOnnxRuntimeGenAIChatCompletion to accept the providers parameter.
• New Demo Project: Created OnnxWithProviderChoice demo showcasing the new provider configuration API
• Package Configuration: Add the Microsoft.ML.OnnxRuntime.Gpu package version in the Directory.Packages.props

Design Approach:

The implementation leverages ONNX Runtime GenAI's existing Config API to programmatically set providers and their options. The Provider class provides a clean abstraction for specifying provider ID (e.g., "cuda", "cpu") and custom options. During service initialization, the providers are configured using the underlying ONNX Runtime GenAI configuration system.

Usage Example:

builder.AddOnnxRuntimeGenAIChatCompletion(
    modelId: "onnx",
    modelPath: modelPath,
    providers: [new Provider { Id = "cuda" }]
);

Backward Compatibility:
This change maintains full backward compatibility. Existing code continues to work without modification, and the manual genai_config.json approach remains supported.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[rogerbarreto]

@loicbtd Thanks for the contribution, I added some extra updates to this PR related to your change and other outstanding changes I had plan myself to add to the connector. Overall LTGM.

[loicbtd]

Thanks for the update 👍