Add drive metrics in metrics-v3 (#19452)

Add following metrics:

- used_inodes
- total_inodes
- healing
- online
- reads_per_sec
- reads_kb_per_sec
- reads_await
- writes_per_sec
- writes_kb_per_sec
- writes_await
- perc_util

To be able to calculate the `per_sec` values, we capture the IOStats-related 
data in the beginning (along with the time at which they were captured), 
and compare them against the current values subsequently. This is because 
dividing by "time since server uptime." doesn't work in k8s environments.

cmd/metrics-v3.go

@@ -117,15 +117,28 @@ func newMetricGroups(r *prometheus.Registry) *metricsV3Collection {
 			driveUsedBytesMD,
 			driveFreeBytesMD,
 			driveTotalBytesMD,
+			driveUsedInodesMD,
 			driveFreeInodesMD,
+			driveTotalInodesMD,
 			driveTimeoutErrorsMD,
 			driveAvailabilityErrorsMD,
 			driveWaitingIOMD,
 			driveAPILatencyMD,
+			driveHealingMD,
+			driveOnlineMD,
 
 			driveOfflineCountMD,
 			driveOnlineCountMD,
 			driveCountMD,
+
+			// iostat related
+			driveReadsPerSecMD,
+			driveReadsKBPerSecMD,
+			driveReadsAwaitMD,
+			driveWritesPerSecMD,
+			driveWritesKBPerSecMD,
+			driveWritesAwaitMD,
+			drivePercUtilMD,
 		},
 		loadDriveMetrics,
 	)