Add Support for Cache and S3 related metrics in Prometheus endpoint (#8591)

This PR adds support below metrics

- Cache Hit Count
- Cache Miss Count
- Data served from Cache (in Bytes)
- Bytes received from AWS S3
- Bytes sent to AWS S3
- Number of requests sent to AWS S3

Fixes #8549

cmd/xl-v1.go

@@ -200,3 +200,9 @@ func getStorageInfo(disks []StorageAPI) StorageInfo {
 func (xl xlObjects) StorageInfo(ctx context.Context) StorageInfo {
 	return getStorageInfo(xl.getDisks())
 }
+
+// GetMetrics - no op
+func (xl xlObjects) GetMetrics(ctx context.Context) (*Metrics, error) {
+	logger.LogIf(ctx, NotImplemented{})
+	return &Metrics{}, NotImplemented{}
+}