monitoring: add exportarr for radarr/sonarr metrics

Add prometheus exportarr exporters for Radarr and Sonarr media
services. Runs on monitoring01, queries remote APIs.

- Radarr exporter on port 9708
- Sonarr exporter on port 9709
- API keys fetched from Vault

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

services/monitoring/default.nix

@@ -5,6 +5,7 @@
     ./grafana.nix
     ./prometheus.nix
     ./blackbox.nix
+    ./exportarr.nix
     ./pve.nix
     ./alerttonotify.nix
     ./pyroscope.nix