Add WithHttpHealthCheck remarks and Debug.Assert for external services (#10524)

[alirezafzali]

Description

Follow-up on review comments from #10493 for ExternalServiceResource.WithHttpHealthCheck (#10524).

Changes:

• Expand XML <remarks> on WithHttpHealthCheck to document static URLs (AddUrlGroup at configuration time) vs. parameter-based URLs (ParameterUriHealthCheck with GetValueAsync on each probe).
• Add a Debug.Assert that either Uri or UrlParameter is set, consistent with AddExternalServiceImpl.

Motivation: The async parameter health-check behavior was added in #10493; this PR completes the remaining documentation and debug-assert feedback from that review. No behavioral changes.

Dependencies: None.

Fixes #10524

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
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
  • No

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds clarity and a guardrail around how WithHttpHealthCheck behaves depending on whether an external service uses a static URI vs. a parameter-resolved URI.

Changes:

• Expanded XML docs to describe health check registration behavior for static URIs vs. URL parameters.
• Added a Debug.Assert to enforce that either Uri or UrlParameter is present before registering the health check.

[github-actions]

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://raw.githubusercontent.com/microsoft/aspire/main/eng/scripts/get-aspire-cli-pr.sh | bash -s -- 17281

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/microsoft/aspire/main/eng/scripts/get-aspire-cli-pr.ps1) } 17281"

[DamianEdwards]

Thanks!