Copy the traceparent header between calls to show how tracing works across multiple API calls

[msfussell]

This is for updating the Hello-World and Hello-Kubernetes quickstarts to show tracing across two independent API calls. A small change in the Node application can show this end to end by copying the trace header as shown below.

app.post('/neworder', (req, res) => {
    const data = req.body.data;
    const traceparent = req.headers.traceparent;
    const orderId = data.orderId;
    console.log("Got a new order! Order ID: " + orderId + " traceparent: " + traceparent);

    const state = [{
        key: "order",
        value: data
    }];

    fetch(stateUrl, {
        method: "POST",
        body: JSON.stringify(state),
        headers: {
            "Content-Type": "application/json",
            "traceparent": traceparent  //copy the traceparent header from the incoming request to trace the call to state management API
        }
    }).then((response) => {
        if (!response.ok) {
            throw "Failed to persist state.";
        }

Then instead of this

you get this for zipkin tracing.

This will work for both self hosted and K8s. At the same time it is worth updating the Observability Tutorial to show this end to end tracing since this not that well described in the docs today.

[sicoyle]

Need to audit the docs and add a section on how to propagate the headers for tracing. Add code samples to docs.

Could add quickstarts example that shows how to do this.