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/handler-utils.go

@@ -348,6 +348,39 @@ func httpTraceHdrs(f http.HandlerFunc) http.HandlerFunc {
 	}
 }
 
+func collectAPIStats(api string, f http.HandlerFunc) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+
+		isS3Request := !strings.HasPrefix(r.URL.Path, minioReservedBucketPath)
+		apiStatsWriter := &recordAPIStats{w, UTCNow(), false, 0, isS3Request}
+
+		// Time start before the call is about to start.
+		tBefore := UTCNow()
+
+		if isS3Request {
+			globalHTTPStats.currentS3Requests.Inc(api)
+		}
+		// Execute the request
+		f.ServeHTTP(apiStatsWriter, r)
+
+		if isS3Request {
+			globalHTTPStats.currentS3Requests.Dec(api)
+		}
+
+		// Firstbyte read.
+		tAfter := apiStatsWriter.TTFB
+
+		// Time duration in secs since the call started.
+		//
+		// We don't need to do nanosecond precision in this
+		// simply for the fact that it is not human readable.
+		durationSecs := tAfter.Sub(tBefore).Seconds()
+
+		// Update http statistics
+		globalHTTPStats.updateStats(api, r, apiStatsWriter, durationSecs)
+	}
+}
+
 // Returns "/bucketName/objectName" for path-style or virtual-host-style requests.
 func getResource(path string, host string, domains []string) (string, error) {
 	if len(domains) == 0 {