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/posix.go

@@ -309,10 +309,11 @@ func (s *posix) IsOnline() bool {
 // DiskInfo is an extended type which returns current
 // disk usage per path.
 type DiskInfo struct {
-	Total    uint64
-	Free     uint64
-	Used     uint64
-	RootDisk bool
+	Total        uint64
+	Free         uint64
+	Used         uint64
+	RootDisk     bool
+	RelativePath string
 }
 
 // DiskInfo provides current information about disk space usage,
@@ -346,12 +347,14 @@ func (s *posix) DiskInfo() (info DiskInfo, err error) {
 	if err != nil {
 		return info, err
 	}
+	localPeer := GetLocalPeer(globalEndpoints)
 
 	return DiskInfo{
-		Total:    di.Total,
-		Free:     di.Free,
-		Used:     used,
-		RootDisk: rootDisk,
+		Total:        di.Total,
+		Free:         di.Free,
+		Used:         used,
+		RootDisk:     rootDisk,
+		RelativePath: localPeer + s.diskPath,
 	}, nil
 }