Add nomad env to envoy bootstrap

[jorgemarey]

Just saw #12543 .We are doing things a bit different in a fork we have. This PR takes a different aproach and adds enviroment variables to the envoy boostrap hook. This along with hashicorp/consul#13049 allow us to configure things like the following in the consul 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}",
      ]
}

This can also be set on the nomad sidecar configuration.

[Amier3]

We might want to put a hold on this pending the changes in hashicorp/consul#13049

[shoenig]

Unless I'm mistaken, closed by #14311

[jorgemarey]

Hi @shoenig. I guess that this specific case presented in the issue (adding the stats tags to envoy) is solved by #14311, but I don't think it's the only use case for passing the NOMAD_ environment variables to the envoy task. I think that providing those values to envoy could allow users to better modify their escape-hatchs if necesary. What do you think?

[shoenig]

Sounds reasonable enough to me ~

[shoenig]

LGTM

[github-actions]

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