Add NuGet publishing workflow with OIDC authentication and increment package version

[Copilot]

Overview

This PR implements automated NuGet package publishing to nuget.org using GitHub Actions with OIDC-based trusted publishing, following the official Microsoft documentation at https://learn.microsoft.com/en-us/nuget/nuget-org/trusted-publishing#github-actions-setup.

Changes

1. GitHub Actions Workflow

Created .github/workflows/publish-nuget.yml that:

• Triggers automatically when a GitHub release is published
• Uses OIDC trusted publishing for secure authentication (no API key secrets required)
• Builds the project in Release configuration
• Packs the NuGet package
• Publishes to nuget.org using --api-key az for OIDC authentication

The workflow includes the required id-token: write permission to enable OIDC token generation, as specified in the Microsoft trusted publishing documentation.

2. Package Version Increment

Updated the package version in ContosoMCP/ContosoMCP.csproj from 0.1.0-beta to 0.2.0-beta.

Benefits

• Enhanced Security: OIDC authentication eliminates the need to store long-lived API keys as GitHub secrets
• Automation: Packages are automatically published when releases are created
• Reliability: Uses official GitHub Actions and .NET tooling with proper build/test/pack workflow
• Maintainability: Clean, well-structured workflow that's easy to understand and modify

Next Steps

Before the workflow can publish packages, the repository owner needs to:

1. Sign in to nuget.org
2. Navigate to the ContosoMCPServer package settings
3. Under "Trusted Publishers", add a new GitHub Actions publisher with:
   • Repository owner: seaniyer
   • Repository name: ContosoMCP
   • Workflow name: publish-nuget.yml
   • Environment: (leave empty)

Once configured, simply create and publish a GitHub release (e.g., tag v0.2.0-beta) to trigger the workflow and publish the package to nuget.org.

Testing

• ✅ Build verified successfully with new version
• ✅ Package creation tested (ContosoMCPServer.0.2.0-beta.nupkg generated)
• ✅ Workflow YAML validated with yamllint

Original prompt

Create a workflow to push the nuget package from this project to nuget.org. Be sure to set it up to publish using OIDC following the instructions in https://learn.microsoft.com/en-us/nuget/nuget-org/trusted-publishing#github-actions-setup
Increment the package version

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[seaniyer]

@copilot continue and finish the changes requested in the previous prompt