fix: annotate healthz endpoint handler

[ZY-Ang]

References to other Issues or PRs

• Add WithHealthzEndpoint as ServeMuxOption to register a /healthzendpoint #2319
• feature/custom HTTP health check endpoint #2587

Have you read the Contributing Guidelines?

Yes

Brief description of what is fixed or changed

Enhanced Context Annotation for Health Check Endpoint

What's Changed

Added proper context annotation to the health check endpoint handler, including:

• GRPC method name annotation (grpc_health_v1.Health_Check_FullMethodName)
• HTTP path pattern information
• Server metadata handling for GRPC headers and trailers

Why

The current implementation passes the raw context directly to the health check client without any GRPC Gateway-specific annotations. This means:

1. Observability tools and middleware can't properly trace the GRPC method being called
2. The HTTP endpoint information is not propagated through the context
3. GRPC metadata (headers/trailers) are not being handled

Benefits

• Improved observability: Tracing and monitoring tools can now see the full request path from HTTP to GRPC
• Consistent behavior: The health endpoint now follows the same context annotation pattern as other endpoints
• Better debugging: Full context information available throughout the request lifecycle
• Proper metadata handling: GRPC headers and trailers are now properly managed

Testing

The changes maintain existing functionality while adding context enrichment. All existing health check behaviors remain unchanged.

Other comments

[johanbrandhorst]

Thanks, this looks great!

[johanbrandhorst]

Looks like we need to generate the bazel files, try running the command in CONTRIBUTING.md

[ZY-Ang]

@johanbrandhorst thanks and fixed - I might have missed a couple of errors the first time I ran the commands.

[johanbrandhorst]

Thanks!