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

pkg/madmin/top-commands.go

@@ -54,10 +54,10 @@ func (l LockEntries) Swap(i, j int) {
 
 // TopLocks - returns the oldest locks in a minio setup.
 func (adm *AdminClient) TopLocks() (LockEntries, error) {
-	// Execute GET on /minio/admin/v1/top/locks
+	// Execute GET on /minio/admin/v2/top/locks
 	// to get the oldest locks in a minio setup.
 	resp, err := adm.executeMethod("GET",
-		requestData{relPath: "/v1/top/locks"})
+		requestData{relPath: adminAPIPrefix + "/top/locks"})
 	defer closeResponse(resp)
 	if err != nil {
 		return nil, err