[FEATURE] OFREP evaluation is missing tracing semconv attributes

Requirements

The ofrep handler is missing the least necessary data for attributes described here (feature_flag.key and feature_flag.result.variant) compared to the http\grpc evaluators.

https://github.com/open-feature/flagd/blob/7c6d46533bd76ff6637f07a28e3d2d71299b8c16/flagd/pkg/service/flag-evaluation/ofrep/handler.go#L75

func (h *handler) HandleFlagEvaluation(w http.ResponseWriter, r *http.Request) {
	requestID := xid.New().String()
	defer h.Logger.ClearFields(requestID)

	// obtain flag key
	vars := mux.Vars(r)
	if vars == nil {
		h.writeJSONToResponse(
			http.StatusInternalServerError,
			ofrep.InternalError{ErrorDetails: "failed to obtain the flag key from the request"}, w)
		return
	}

	flagKey := vars[key]
	request, err := extractOfrepRequest(r)
	if err != nil {
		h.writeJSONToResponse(http.StatusBadRequest, ofrep.ContextErrorResponseFrom(flagKey), w)
		return
	}
	evaluationContext := flagdContext(h.Logger, requestID, request, h.contextValues, r.Header, h.headerToContextKeyMappings)
	selectorExpression := r.Header.Get(service.FLAGD_SELECTOR_HEADER)
	selector := store.NewSelector(selectorExpression)
	ctx := context.WithValue(r.Context(), store.SelectorContextKey{}, selector)
	ctx, span := h.tracer.Start(ctx, "handleFlagEvaluation", trace.WithSpanKind(trace.SpanKindServer))
	evaluation := h.evaluator.ResolveAsAnyValue(ctx, requestID, flagKey, evaluationContext)
	span.SetAttributes(telemetry.SemConvFeatureFlagAttributes(flagKey, evaluation.Variant)...)
	defer span.End()
	if evaluation.Error != nil {
		span.SetStatus(codes.Error, "handleFlagEvaluation error")
		span.RecordError(evaluation.Error)
		status, evaluationError := ofrep.EvaluationErrorResponseFrom(evaluation)
		h.writeJSONToResponse(status, evaluationError, w)
	} else {
		h.writeJSONToResponse(http.StatusOK, ofrep.SuccessResponseFrom(evaluation), w)
	}
}

Something like that should yield the desired outcome
before

after

Start in flagd/pkg/service/flag-evaluation/ofrep/handler.go at HandleFlagEvaluation, then compare the tracing attributes produced by the http and grpc evaluators. Ensure OFREP evaluation spans include the feature flag key and result variant attributes, and verify the resulting trace matches the documented semconv outcome.