Add opentracing integration

[austenLacy]

These changes allow for a rollbar.js user to inject an OpenTracing tracer object as a configuration option.

Whenever an error or message is logged via Rollbar we will check if the client has as tracer set. If that tracer is valid then we set the new occurrence UUID as metadata on the opentracing span as well as add the opentracing trace ID and span ID to the occurrence as custom metadata.

Implementation Examples

---

automatic instrumentation

const tracer = require('ls-trace').init({
  experimental: { b3: true }
});

const Rollbar = require('rollbar');
const rollbar = new Rollbar({
  accessToken: process.env.ROLLBAR_ACCESS_TOKEN,
  captureUncaught: true,
  captureUnhandledRejections: true,
  tracer: tracer // Add tracer here...
});

manual instrumentation

app.get('/hello', function getHello(req, res) {
  let span = null;

  try {
    const name = req.query.name;
    const parentSpan = tracer.scope().active();
    span = tracer.startSpan('getHelloWorld', { childOf: parentSpan });

    if (name && name.toLowerCase() === 'error') {
      throw new Error("Can't say hello to an error!");
    }

    res.status(200).send({
      message: `Hello ${name ? name : 'world'}!`
    });

    span.finish();
  } catch (err) {
    rollbar.error(err, req, { opentracing_span_id: span.context().toSpanId(), opentracing_trace_id: span.context().toTraceId() }, (internalRbErr, rbRes) => {
      if (internalRbErr) {
        console.error(internalRbErr);
      } else {
        if (span) {
          span.setTag('rollbar_uuid', rbRes.uuid);
          span.setTag('has_rollbar_error', true);
          span.finish();
        }
      }
    });

    res.status(500).send({ error: err.message });
  }
});

[waltjones]

Looks good. 👍

[waltjones]

Changes look good. 👍

[Renatopster]

This results in duplicated properties in Occurrences view... Could we revert this part?

[waltjones]

I think the intent is to support the custom key as defined by the API. https://explorer.docs.rollbar.com/#operation/create-item

Maybe a config option for this is the best way to meet both needs.