docs(example): demonstrate OpenTelemetry span kind usage

Author: alessandrobologna

examples/opentelemetry-tracing/src/main.rs

@@ -1,13 +1,15 @@
 use lambda_runtime::{
     layers::{OpenTelemetryFaasTrigger, OpenTelemetryLayer as OtelLayer},
-    LambdaEvent, Runtime,
+    LambdaEvent, Runtime, tracing::Span
 };
 use opentelemetry::trace::TracerProvider;
 use opentelemetry_sdk::{runtime, trace};
 use tower::{service_fn, BoxError};
 use tracing_subscriber::prelude::*;
 
 async fn echo(event: LambdaEvent<serde_json::Value>) -> Result<serde_json::Value, &'static str> {
+    let span = Span::current();
+    span.record("otel.kind", "SERVER");
     Ok(event.payload)
 }