[release/9.4] Add GitHub Models integration (#10170)

[eerhardt]

Backport of #10170 to release/9.4

/cc @sebastienros

Customer Impact

Customers can use GitHub models easily in their Aspire applications.

Testing

Manual and new unit tests added.

Risk

Almost none. Just a new integration - no product changes outside of the new integration.

Regression?

No

Description

Adds a new hosting integration for GitHub Models.

Fixes #9569 #7649

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
    • If yes, did you have an API Review for it?
      • Yes
      • No
    • Did you add <remarks /> and <code /> elements on your triple slash comments?
      • Yes
      • No
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
    • If yes, have you done a threat model and had a security review?
      • Yes
      • No
  • No
• Does the change require an update in our Aspire docs?
  • Yes
    • [New article]: GitHub Models integration dotnet/docs-aspire#3913
  • No

[Copilot]

Pull Request Overview

Backports the GitHub Models hosting integration to release/9.4, enabling Aspire applications to configure and use GitHub Models resources via a new extension, resource type, health check, and accompanying tests.

• Introduces GitHubModelsExtensions, GitHubModelResource, and GitHubModelsHealthCheck in the hosting library
• Adds comprehensive unit tests in Aspire.Hosting.GitHub.Models.Tests
• Updates README and playground projects to demonstrate end-to-end usage

Reviewed Changes

Copilot reviewed 28 out of 29 changed files in this pull request and generated 2 comments.

File	Description
src/Aspire.Hosting.GitHub.Models/GitHubModelsExtensions.cs	Extension methods to add/configure GitHub Models resources and health checks
src/Aspire.Hosting.GitHub.Models/GitHubModelsHealthCheck.cs	IHealthCheck implementation querying the GitHub Models API
src/Aspire.Hosting.GitHub.Models/GitHubModelResource.cs	Resource class exposing model, organization, key, and connection string
tests/Aspire.Hosting.GitHub.Models.Tests/GitHubModelsExtensionTests.cs	Unit tests covering endpoints, API key, organization, and health check annotation

Comments suppressed due to low confidence (2)

src/Aspire.Hosting.GitHub.Models/GitHubModelsExtensions.cs:40

• For consistency with official branding, consider updating "Github Models" to "GitHub Models".

                        new(CustomResourceKnownProperties.Source, "Github Models")

src/Aspire.Hosting.GitHub.Models/GitHubModelsHealthCheck.cs:19

• The _result field is accessed without synchronization and could be set concurrently on multiple threads. Consider making access thread-safe (e.g., using a lock or Interlocked.CompareExchange).

    private HealthCheckResult? _result;