Add datadog plugin for tracing

[kalfonso]

Signed-off-by: Karel Alfonso Sague kalfonso@squareup.com

[kalfonso]

@systay you might be familiar with this change

[tirsen]

I think we've had different opinions on dependencies on these commercial third parties. That said DataDog is pretty popular and if you don't use it there is only a tiny bit of overhead for the dependency.

[systay]

LGTM

[deepthi]

I think we've had different opinions on dependencies on these commercial third parties. That said DataDog is pretty popular and if you don't use it there is only a tiny bit of overhead for the dependency.

@kalfonso FTR, can you document the change in binary sizes /docker images here?
Also are there any license implications from the packages we are importing?

[derekperkins]

What about hiding these behind build tags?

[sougou]

I took a look at the implementation. Looks lightweight, and it ironically depends on opentracing, which we already depend on.

So, lets move ahead with this. If this becomes a problem in the future, we can reconsider our options.