Add Namespace, Job and Group to envoy stats

[jorgemarey]

This PR adds more tags (nomad namespace, job and group) to the envoy stats tags.
It's useful when performing scaling based on envoy request being able to filter the service by nomad job/group.

Follows the work done in #12543

[tgross]

Thanks for the PR @jorgemarey! I've left some comments for discussion.

[jorgemarey]

Thanks @tgross for taking the time to review this. I'll update the PR with the suggested changes as soon as I can!

[tgross]

Hi @jorgemarey! Thanks for your patience on this. The updates you've done here LGTM 👍 . I'm going to push a changelog entry on top of the PR, rebase on main, and fix the merge conflicts and then we'll get this merged.

[vercel]

Deployment failed with the following error:

The provided GitHub repository does not contain the requested branch or commit reference. Please ensure the repository is not empty.

[tgross]

Merged! This will ship in Nomad 1.4.0

[github-actions]

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