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/peer-rest-server.go

@@ -50,11 +50,11 @@ func getServerInfo() (*ServerInfoData, error) {
 	if objLayer == nil {
 		return nil, errServerNotInitialized
 	}
+
 	// Server info data.
 	return &ServerInfoData{
-		StorageInfo: objLayer.StorageInfo(context.Background()),
-		ConnStats:   globalConnStats.toServerConnStats(),
-		HTTPStats:   globalHTTPStats.toServerHTTPStats(),
+		ConnStats: globalConnStats.toServerConnStats(),
+		HTTPStats: globalHTTPStats.toServerHTTPStats(),
 		Properties: ServerProperties{
 			Uptime:       UTCNow().Sub(globalBootTime),
 			Version:      Version,