Add lightweight health and resilience sample

[balajibashyam]

Summary

Adds a minimal .NET 10 companion sample for the .NET 8 Cloud-Native: Health Probes, Polly Resilience & Zero-Downtime Kubernetes Deployments tutorial.

What's included

• New sample: cloud-native/health-resilience-zero-downtime — 13 files

  • Tagged liveness and readiness health checks
  • Structured JSON health responses
  • Shutdown readiness draining via ShutdownReadinessService
  • Typed PaymentGatewayClient with Microsoft.Extensions.Http.Resilience 10.8.0
  • HTTP 503 retry (2 retries, jittered exponential backoff)
  • Circuit breaker (3 qualifying 503s opens, 10s break)
  • Attempt timeout (2 seconds)
  • Non-retriable HTTP 400 (1 attempt, no retry)
  • Deterministic in-process SimulatedPaymentHandler
  • 6 integration tests

• Root README: New sample row + updated cloud-native tree (both siblings)

• GitHub Actions: New test-health-resilience-shutdown job; path filters updated

Deliberately omitted (stays in the full tutorial)

Databases, queues, migrations, background processing, Docker, Kubernetes, OpenTelemetry, load testing, secrets, production rollout.

Versions

• .NET SDK: 10.0.302
• Microsoft.Extensions.Http.Resilience: 10.8.0
• Microsoft.AspNetCore.Mvc.Testing: 10.0.10
• Microsoft.NET.Test.Sdk: 18.8.1
• xunit.v3: 3.2.2
• xunit.runner.visualstudio: 3.1.5

Validation

• dotnet restore — passed
• dotnet build --configuration Release — passed (0 errors, 0 warnings)
• dotnet test — passed (6/6)
• Normal health — all 200 OK (structured JSON)
• Retry success — 3 attempts, 200 OK
• Non-retriable 400 — 1 attempt, 400 Bad Request
• Circuit breaker — first: 3 attempts/503, second: 0 attempts/503 circuit open
• Security scan — clean