Add more complete trace example

[kintel]

The current trace example is very minimal.
We should add a more complete example that:

• Is a service
• Makes an external HTTP request
• Uses auto-instrumentation to create both server and client spans
• Uses trace context from incoming HTTP headers

[mayurkale22]

Just so you know: we have a couple of examples in the main OpenTelemetry repo: https://github.com/open-telemetry/opentelemetry-js/tree/master/examples. Maybe, we can point everyone to use those examples, WDYT?

[kintel]

Yeah, I don't think we need to be exhaustive here, but since none of the upstream examples will work out of the box with Cloud Trace, it would be nice with at least one more complete example here.
The goal would be to provide something that works out of the box to help customers get started.

These examples could live in https://github.com/GoogleCloudPlatform/nodejs-docs-samples, but I'm not 100% certain what examples should go where.

[dashpole]

triaging. It is a good suggestion, but not urgent.

[dashpole]

Still not urgent