tracing: span kind not set

[wkloucek]

Is your feature request related to a problem? Please describe.

Our spans have no kind set. Read more about span kinds: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/api.md#spankind

Because of this missing span kind, some tools might not work properly, eg. Jaeger SPM (https://www.jaegertracing.io/docs/1.42/spm/#serviceoperation-missing-in-monitor-tab)

Describe the solution you'd like

Have a kind set on our spans.

Additional context

Example how to set it:

diff --git a/services/proxy/pkg/proxy/proxy.go b/services/proxy/pkg/proxy/proxy.go
index 4e773ca1f..aeaa4c9c6 100644
--- a/services/proxy/pkg/proxy/proxy.go
+++ b/services/proxy/pkg/proxy/proxy.go
@@ -90,7 +90,12 @@ func (p *MultiHostReverseProxy) ServeHTTP(w http.ResponseWriter, r *http.Request
        )
 
        tracer := proxytracing.TraceProvider.Tracer("proxy")
-       ctx, span = tracer.Start(ctx, fmt.Sprintf("%s %v", r.Method, r.URL.Path))
+
+       spanOpts := []trace.SpanStartOption{
+               trace.WithSpanKind(trace.SpanKindServer),
+       }
+
+       ctx, span = tracer.Start(ctx, fmt.Sprintf("%s %v", r.Method, r.URL.Path), spanOpts...)
        defer span.End()
 
        span.SetAttributes(