Add per-pod GPU memory metrics exporter

- Add DaemonSet that runs on GPU node and exposes Prometheus metrics
- Uses nvidia-smi to collect per-process GPU memory usage
- Maps PIDs to container IDs via /proc/<pid>/cgroup
- Exposes gpu_pod_memory_used_bytes metric at :9401/metrics
- Add Prometheus scrape config for gpu-pod-memory job

[ci skip]

modules/kubernetes/monitoring/prometheus_chart_values.tpl

@@ -623,4 +623,9 @@ extraScrapeConfigs: |
         action: replace
         regex: '(.*)'
         replacement: 'nvidia_tesla_t4_$${1}'
+  - job_name: 'gpu-pod-memory'
+    static_configs:
+        - targets:
+          - "gpu-pod-exporter.nvidia.svc.cluster.local"
+    metrics_path: '/metrics'