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/group-commands.go

@@ -41,11 +41,11 @@ func (adm *AdminClient) UpdateGroupMembers(g GroupAddRemove) error {
 	}
 
 	reqData := requestData{
-		relPath: "/v1/update-group-members",
+		relPath: adminAPIPrefix + "/update-group-members",
 		content: data,
 	}
 
-	// Execute PUT on /minio/admin/v1/update-group-members
+	// Execute PUT on /minio/admin/v2/update-group-members
 	resp, err := adm.executeMethod("PUT", reqData)
 
 	defer closeResponse(resp)
@@ -74,7 +74,7 @@ func (adm *AdminClient) GetGroupDescription(group string) (*GroupDesc, error) {
 	v := url.Values{}
 	v.Set("group", group)
 	reqData := requestData{
-		relPath:     "/v1/group",
+		relPath:     adminAPIPrefix + "/group",
 		queryValues: v,
 	}
 
@@ -104,7 +104,7 @@ func (adm *AdminClient) GetGroupDescription(group string) (*GroupDesc, error) {
 // ListGroups - lists all groups names present on the server.
 func (adm *AdminClient) ListGroups() ([]string, error) {
 	reqData := requestData{
-		relPath: "/v1/groups",
+		relPath: adminAPIPrefix + "/groups",
 	}
 
 	resp, err := adm.executeMethod("GET", reqData)
@@ -146,7 +146,7 @@ func (adm *AdminClient) SetGroupStatus(group string, status GroupStatus) error {
 	v.Set("status", string(status))
 
 	reqData := requestData{
-		relPath:     "/v1/set-group-status",
+		relPath:     adminAPIPrefix + "/set-group-status",
 		queryValues: v,
 	}