Add nixos-exporter prometheus exporter to track NixOS generation metrics
and flake revision status across all hosts.
Changes:
- Add nixos-exporter flake input
- Add commonModules list in flake.nix for modules shared by all hosts
- Enable nixos-exporter in system/monitoring/metrics.nix
- Configure Prometheus to scrape nixos-exporter on all hosts
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Torjus Håkestad
97ff774d3f
