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/admin-handlers_test.go

@@ -396,7 +396,7 @@ func testServiceSignalReceiver(cmd cmdType, t *testing.T) {
 func getServiceCmdRequest(cmd cmdType, cred auth.Credentials) (*http.Request, error) {
 	queryVal := url.Values{}
 	queryVal.Set("action", string(cmd.toServiceAction()))
-	resource := "/minio/admin/v1/service?" + queryVal.Encode()
+	resource := adminAPIPathPrefix + "/service?" + queryVal.Encode()
 	req, err := newTestRequest(http.MethodPost, resource, 0, nil)
 	if err != nil {
 		return nil, err
@@ -465,7 +465,7 @@ func buildAdminRequest(queryVal url.Values, method, path string,
 	contentLength int64, bodySeeker io.ReadSeeker) (*http.Request, error) {
 
 	req, err := newTestRequest(method,
-		"/minio/admin/v1"+path+"?"+queryVal.Encode(),
+		adminAPIPathPrefix+path+"?"+queryVal.Encode(),
 		contentLength, bodySeeker)
 	if err != nil {
 		return nil, err