Support DogStatsD for telemetry

[justinwalz]

It would be nice to have this feature implemented for vault as well https://www.consul.io/docs/agent/options.html#telemetry-dogstatsd_addr

It sends similar metrics to the already implemented statsd_address, but adds tagging and support for other datadog features.

[justinwalz]

Here's the relevant PR for consul, seems like it's already implemented in go-metrics: https://github.com/hashicorp/consul/pull/1293/files

[Kahn]

This would be awesome huge +1. I was surprised to see it missing from Vault telemetry since I had just created Consul config.

We use https://github.com/atlassian/gostatsd and need to use tagged metrics for our deployment which the native statsd telemetry doesn't seem to support.