monitoring02: add Loki service

Add standalone Loki service module (services/loki/) with same config as
monitoring01 and import it on monitoring02. Update Grafana Loki datasource
to localhost. Defer Tempo and Pyroscope migration (not actively used).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

hosts/monitoring02/default.nix

@@ -3,5 +3,6 @@
     ./configuration.nix
     ../../services/grafana
     ../../services/victoriametrics
+    ../../services/loki
   ];
 }