[Feature] Support OpenTracing

[jebbench]

I'm looking to add tracing to our application using the OpenTracing API but I can't see a way to intercept commands sent to Arango other than wrapping every call to the driver manually.

In an ideal world the Arango driver would support tracing natively or provide a supported method of easily adding tracing.

[rashtao]

related slack thread: https://arangodb-community.slack.com/archives/C07NV9NAH/p1573818483191000

Also consider: https://opentelemetry.io