Add expanding on environment for stats tags

[jorgemarey]

This PR ands enviroment expansion for envoy stats tags. This, along with hashicorp/nomad#12959 will allow us to do things like in the proxy configuration:

kind = "proxy-defaults"
name = "global"

Config {
      envoy_dogstatsd_url = "udp://172.26.64.1:9125"
      envoy_stats_tags = [
        "alloc_id=${NOMAD_ALLOC_ID}",
        "nomad_group=${NOMAD_GROUP_NAME}",
        "nomad_job=${NOMAD_JOB_NAME}",
        "nomad_namespace=${NOMAD_NAMESPACE}",
      ]
}

[Amier3]

Hey @jorgemarey

Thanks for making this PR! The team talked about this today and we really like the change, but we're not sure if this should be set on the proxy-defaults layer ( mainly because adding new variables would require a envoy restart, which might lead to a bad UX ). There's also some security considerations we have to make.

We'll sync up on this again shortly and hopefully get you some feedback back on how we'd like to approach this. Thank you again!

[github-actions]

This pull request has been automatically flagged for inactivity because it has not been acted upon in the last 60 days. It will be closed if no new activity occurs in the next 30 days. Please feel free to re-open to resurrect the change if you feel this has happened by mistake. Thank you for your contributions.

[jorgemarey]

Hi @Amier3 any news on this?

[jorgemarey]

I think that if you don't consider this to be OK. We can close this in favor of hashicorp/nomad#14311

[david-yu]

Hi @jorgemarey I'll go ahead and close this in favor of the Nomad PR you referenced. We believe that is probably a better path forward t get those stats tags for Nomad in.

[jorgemarey]

Hi @david-yu, Yeah, you're right, it looks like a better path.