…t#12861)

### Motivation and Context

<!-- Thank you for your contribution to the semantic-kernel repo!
Please help reviewers and future users, providing the following
information:
  1. Why is this change required?
  2. What problem does it solve?
  3. What scenario does it contribute to?
  4. If it fixes an open issue, please link to the issue here.
-->

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 microsoft#12828 

### Description

<!-- Describe your changes, the overall approach, the underlying design.
These notes will help understanding how your code works. Thanks! -->

**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:**
```csharp
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

<!-- Before submitting this PR, please make sure: -->

- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

---------

Co-authored-by: Roger Barreto <19890735+rogerbarreto@users.noreply.github.com>

…t#12861)

### Motivation and Context

<!-- Thank you for your contribution to the semantic-kernel repo!
Please help reviewers and future users, providing the following
information:
  1. Why is this change required?
  2. What problem does it solve?
  3. What scenario does it contribute to?
  4. If it fixes an open issue, please link to the issue here.
-->

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 microsoft#12828 

### Description

<!-- Describe your changes, the overall approach, the underlying design.
These notes will help understanding how your code works. Thanks! -->

**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:**
```csharp
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

<!-- Before submitting this PR, please make sure: -->

- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

---------

Co-authored-by: Roger Barreto <19890735+rogerbarreto@users.noreply.github.com>