Datadog exporter doesn't send resources from trace::Config

[bnjjj]

In DatadogExporter resources (https://docs.rs/opentelemetry/latest/opentelemetry/sdk/trace/struct.Config.html#structfield.resource) are not sent to datadog. Only span attributes are sent to Datadog.

[lroux-at-jellysmack]

Hello @bnjjj, I also noticed that as I tried to tag a service-wide version for deployment tracking of my application.
Do you think the way to do it would be to also encode trace::Config::resource in there as span attributes ?

[bnjjj]

@lroux-at-jellysmack I think so :)

[abernix]

Now waiting on #965! Looking forward to this release! 😄