The prometheus metrics refractoring (#8003)

The measures are consolidated to the following metrics

- `disk_storage_used` : Disk space used by the disk.
- `disk_storage_available`: Available disk space left on the disk.
- `disk_storage_total`: Total disk space on the disk.
- `disks_offline`: Total number of offline disks in current MinIO instance.
- `disks_total`: Total number of disks in current MinIO instance.
- `s3_requests_total`: Total number of s3 requests in current MinIO instance.
- `s3_errors_total`: Total number of errors in s3 requests in current MinIO instance.
- `s3_requests_current`: Total number of active s3 requests in current MinIO instance.
- `internode_rx_bytes_total`: Total number of internode bytes received by current MinIO server instance.
- `internode_tx_bytes_total`: Total number of bytes sent to the other nodes by current MinIO server instance.
- `s3_rx_bytes_total`: Total number of s3 bytes received by current MinIO server instance.
- `s3_tx_bytes_total`: Total number of s3 bytes sent by current MinIO server instance.
- `minio_version_info`: Current MinIO version with commit-id.
- `s3_ttfb_seconds_bucket`: Histogram that holds the latency information of the requests.

And this PR also modifies the current StorageInfo queries

- Decouples StorageInfo from ServerInfo .
- StorageInfo is enhanced to give endpoint information.

NOTE: ADMIN API VERSION IS BUMPED UP IN THIS PR

Fixes #7873

cmd/server-startup-msg.go

@@ -188,7 +188,7 @@ func printObjectAPIMsg() {
 func getStorageInfoMsg(storageInfo StorageInfo) string {
 	var msg string
 	if storageInfo.Backend.Type == BackendErasure {
-		diskInfo := fmt.Sprintf(" %d Online, %d Offline. ", storageInfo.Backend.OnlineDisks, storageInfo.Backend.OfflineDisks)
+		diskInfo := fmt.Sprintf(" %d Online, %d Offline. ", storageInfo.Backend.OnlineDisks.Sum(), storageInfo.Backend.OfflineDisks.Sum())
 		msg += color.Blue("Status:") + fmt.Sprintf(getFormatStr(len(diskInfo), 8), diskInfo)
 	}
 	return msg