Add node name in node-exporter metrics

[gdemonet]

Component: node-exporter, prometheus

Why this is needed:

• Enable using node-exporter metrics in prometheus-adapter (see Bump kube-prometheus-stack to 45.5.0 #4017 (comment))
• Exploring node-exporter metrics (e.g. using Grafana Explore tab) would be easier
• Querying these metrics from our UI would avoid retrieving node IPs from Salt (to build the "instance" label as $control_plane_ip:$node_exporter_port)

What should be done:

Current service discovery for node-exporter is only using the Service (so, Endpoints), hence, we don't get node metadata. This SO answer seems to point to a solution (i.e. use kubernetes_sd_configs with node role: https://prometheus.io/docs/prometheus/latest/configuration/configuration/#node).