Add OpenTelemetry Support

[sethmaxwl]

OpenTelemetry should be added to PubSub to provide OpenTracing and OpenCensus functionality as one API and SDK. It would be helpful to use it to trace a message throughout its life cycle. This is being added to the Python Pub/Sub client and would be useful to have in the node client as well.

googleapis/python-pubsub#149

[feywind]

@sethmaxwl You're working on this, right? Just trying to get it assigned to the right person.

[sethmaxwl]

@feywind Yes I am.

[thespacedeck]

I cannot wait for this feature :) Thanks for working on this! It would be great to even pass through your own custom HTTP headers, from where you can set the traceparent property in order to propgate it manually. We're currently doing this with Cloud Tasks and it works great.

[CyberHippo]

Hi,

Thanks for all the good work on supporting OpenTelemetry!

Is the tracing limited to the use of BasicTracerProvider and ConsoleSpanExporter or is it compatible with other tracers/exporters such as the NodeTracerProvider tracer or the CollectorTraceExporter exporter ?