Address comment from Peng

Author: noCharger

flint-core/src/main/java/org/opensearch/flint/core/RestHighLevelClientWrapper.java

@@ -138,7 +138,7 @@ private <T> T execute(String metricNamePrefix, IOCallable<T> operation) throws I
      * @param metricNamePrefix the prefix for the metric name which is used to construct the full metric name for success
      */
     private void recordOperationSuccess(String metricNamePrefix) {
-        String successMetricName = metricNamePrefix + ".200.count";
+        String successMetricName = metricNamePrefix + ".2xx.count";
         MetricsUtil.incrementCounter(successMetricName);
     }
 

flint-core/src/main/java/org/opensearch/flint/core/metrics/MetricsUtil.java

@@ -24,6 +24,13 @@ public final class MetricsUtil {
     private MetricsUtil() {
     }
 
+    /**
+     * Increments the Counter metric associated with the given metric name.
+     * If the counter does not exist, it is created before being incremented.
+     *
+     * @param metricName The name of the metric for which the counter is incremented.
+     *                   This name is used to retrieve or create the counter.
+     */
     public static void incrementCounter(String metricName) {
         Counter counter = getOrCreateCounter(metricName);
         if (counter != null) {