monitoring: enable cadvisor diskIO metrics

Adds diskIO to cadvisor --enable_metrics so per-container disk read/write
(container_fs_reads/writes_bytes_total) is exposed — lets node attribution
name which node is the noisy IO neighbor, not just flag the host.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

monitoring.yml

@@ -188,7 +188,7 @@ services:
   cadvisor:
     image: gcr.io/cadvisor/cadvisor
     container_name: cadvisor
-    command: --enable_metrics=cpu,memory,network,disk --store_container_labels=false --docker_only=true
+    command: --enable_metrics=cpu,memory,network,disk,diskIO --store_container_labels=false --docker_only=true
     volumes:
       - /:/rootfs:ro
       - /var/run:/var/run:ro