feat(observability): add comprehensive monitoring for image generation

- Implement image generation metrics collection and reportz
- Add distributed tracing support for image generation requests
- Integrate OpenInference tracing for OpenAI image gen
- Add API tracing support for image generation endpoints
- Include comprehensive test coverage for observability features

Signed-off-by: Hrushikesh Patil <[email protected]>

Author: nutanix-Hrushikesh

internal/tracing/api/api.go

@@ -16,6 +16,7 @@ import (
 	"go.opentelemetry.io/otel/trace"
 
 	"github.com/envoyproxy/ai-gateway/internal/apischema/openai"
+	openaisdk "github.com/openai/openai-go/v2"
 )
 
 var _ Tracing = NoopTracing{}

internal/tracing/image_generation_span.go

@@ -10,6 +10,7 @@ import (
 	"go.opentelemetry.io/otel/trace"
 
 	tracing "github.com/envoyproxy/ai-gateway/internal/tracing/api"
+	openaisdk "github.com/openai/openai-go/v2"
 )
 
 // Ensure imageGenerationSpan implements ImageGenerationSpan.

internal/tracing/image_generation_tracer.go

@@ -15,6 +15,7 @@ import (
 	"go.opentelemetry.io/otel/trace/noop"
 
 	tracing "github.com/envoyproxy/ai-gateway/internal/tracing/api"
+	openaisdk "github.com/openai/openai-go/v2"
 )
 
 // Ensure imageGenerationTracer implements ImageGenerationTracer.

internal/tracing/openinference/openai/image_generation.go

@@ -17,6 +17,7 @@ import (
 
 	tracing "github.com/envoyproxy/ai-gateway/internal/tracing/api"
 	"github.com/envoyproxy/ai-gateway/internal/tracing/openinference"
+	openaisdk "github.com/openai/openai-go/v2"
 )
 
 // ImageGenerationRecorder implements recorders for OpenInference image generation spans.
@@ -88,7 +89,7 @@ func buildImageGenerationRequestAttributes(req *openaisdk.ImageGenerateParams, b
 	attrs := []attribute.KeyValue{
 		attribute.String(openinference.SpanKind, openinference.SpanKindLLM),
 		attribute.String(openinference.LLMSystem, openinference.LLMSystemOpenAI),
-		attribute.String(openinference.LLMModelName, req.Model),
+		attribute.String(openinference.LLMModelName, string(req.Model)),
 	}
 
 	if config.HideInputs {