Add nomad-state-metrics to third-party exporters

[bhope]

nomad-state-metrics is a Prometheus exporter that exposes HashiCorp Nomad object state as metrics - covering jobs, allocations, nodes, deployments, and evaluations. It fills the observability gap between host-level metrics (node_exporter) and Nomad's built-in process metrics (/v1/metrics) by exposing workload object state as Prometheus gauges.

Inspired by kube-state-metrics.

nomad-state-metrics is also now listed on official Hashicorp Nomad community tools page: https://developer.hashicorp.com/nomad/tools

[bhope]

Hi @jan--f I reopened this with the valid link. The project is actively maintained and has already been recognized by Hashicorp Nomad and officially listed in their community page. I am also working with them to get this listed as official integration.

I would love this to be included in Prometheus exporters list, hence the PR.