re-enable dns as a default plugin

[naseemkullah]

• This only affects the JavaScript OpenTelemetry library
• This may affect other libraries, but I would like to get opinions here first

As per gitter chat with @dyladan and @obecny :

The dns is currently disabled as we need to watch for:

any case where creating a span may result in a DNS request, the DNS request may itself trigger a new trace, which may result in a new DNS request, and so on.

However,

with latest changes ver. 0.11 it should automatically surpress tracing for all exporters

Yes that is an important point. The context property to suppress tracing is set in the span processor

if that is happening for dns you might want to add surpressing manually then so the plugin will not cause creating a new span

and at least for collector I have checked that and it was working fine

I also heard from someone that it worked for zipkin that they weren't seeing recursive http calls

[vmarchaud]

We could totally enable it by default indeed.

[vmarchaud]

I think we can close this @naseemkullah ?