adding labels to Stackdriver metrics

[awolde]

Have a way to add custom labels to stackdriver metrics.

**Alternative:
Using telegraf I can do something like this which is what Im doing for Consul:

telemetry {
  dogstatsd_addr = "localhost:8125"
  disable_hostname = true
  dogstatsd_tags = [ "environment:${env}" ]
}

But I dont want to install telegraf agent on Vault.

This is a sample config in vault.hcl I have:

telemetry {
  stackdriver_project_id = "${project}"
  stackdriver_location = "${region}"
  stackdriver_namespace = "vault-cluster-${env}"
  disable_hostname = true
  enable_hostname_label = true
}

I dont know how the namespace is being used, I changed the namespace to different strings and I cannot filter with the namespace. Maybe having something like
tags = [ "foo:bar" ] in the stackdriver telemetry block would help.

This way we can filter the metrics in any way we like in Stackdriver.