fix: use the correct flag name for allow metric label

It should match the flag definition https://github.com/kubernetes/kubernetes/blob/c15581b277e9e42d830898357fdbd92dcf7981c6/staging/src/k8s.io/component-base/metrics/options.go#L81

Author: yongruilin

content/en/docs/concepts/cluster-administration/system-metrics.md

@@ -193,13 +193,13 @@ Each mapping is of the format `<metric_name>,<label_name>=<allowed_labels>` wher
 The overall format looks like:
 
 ```
---allow-label-value <metric_name>,<label_name>='<allow_value1>, <allow_value2>...', <metric_name2>,<label_name>='<allow_value1>, <allow_value2>...', ...
+--allow-metric-labels <metric_name>,<label_name>='<allow_value1>, <allow_value2>...', <metric_name2>,<label_name>='<allow_value1>, <allow_value2>...', ...
 ```
 
 Here is an example:
 
 ```none
---allow-label-value number_count_metric,odd_number='1,3,5', number_count_metric,even_number='2,4,6', date_gauge_metric,weekend='Saturday,Sunday'
+--allow-metric-labels number_count_metric,odd_number='1,3,5', number_count_metric,even_number='2,4,6', date_gauge_metric,weekend='Saturday,Sunday'
 ```
 
 In addition to specifying this from the CLI, this can also be done within a configuration file. You