Consider moving this package to OTel-Go-Contrib

[jmacd]

This is a nice library for the contrib repository:
https://github.com/open-telemetry/opentelemetry-go-contrib

[marwan-at-work]

@jmacd I'd be happy to move it there, I have a couple of questions:

1. How should the directory structure be? For example: <repo>/exporters/datadog?
2. Should each exporter be its own sub-module (has its own go.mod file), or its own repository?
3. I imagine github.com/open-telemetry/opentelemetry-go-contrib/datadog-exporter is pretty long for a module name, anyway we can make it shorter like using the vanity server that already exists for OT? Something like contrib.opentelemetry.io/go ?

[jmacd]

I've already committed a exporters/metric/dogstatsd, which Chris is evaluating. You might add exporters/metric/datadog, I suggest.