fix(dropwizard5): use locale-independent placeholder keys in GraphiteNamePattern (#2619)

`GraphiteNamePattern.extractParameters` builds its placeholder keys with
`String.format("${%d}", ...)`, so under a default locale with non-ASCII
digits such as ar-EG the first key is `${٠}` and `CustomLabelMapper`
leaves `${0}` in the mapped name and labels (`app_requests_${0}_total`
instead of `app_requests_get_total`). This builds the keys with string
concatenation, which does not depend on the locale, and also covers the
dropwizard module since it uses the same mapper. The new
`GraphiteNamePatternTest` case runs with ar-EG as the default locale and
fails without the fix.

@zeitlinger

Signed-off-by: Sharang Gupta <sharang@sharanggupta.dev>

Author: sharanggupta

prometheus-metrics-instrumentation-dropwizard5/src/main/java/io/prometheus/metrics/instrumentation/dropwizard5/labels/GraphiteNamePattern.java

@@ -71,7 +71,7 @@ Map<String, String> extractParameters(final String metricName) {
     final Map<String, String> params = new HashMap<String, String>();
     if (matcher.find()) {
       for (int i = 1; i <= matcher.groupCount(); i++) {
-        params.put(String.format("${%d}", i - 1), matcher.group(i));
+        params.put("${" + (i - 1) + "}", matcher.group(i));
       }
     }
 

prometheus-metrics-instrumentation-dropwizard5/src/test/java/io/prometheus/metrics/instrumentation/dropwizard5/labels/GraphiteNamePatternTest.java

@@ -6,6 +6,7 @@
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import org.assertj.core.api.Assertions;
 import org.junit.jupiter.api.Test;
@@ -132,6 +133,19 @@ void extractParameters() {
         .isEqualTo(expected);
   }
 
+  @Test
+  void extractParameters_WHEN_DefaultLocaleHasNonAsciiDigits_THEN_ShouldUseAsciiKeys() {
+    Locale defaultLocale = Locale.getDefault();
+    Locale.setDefault(Locale.forLanguageTag("ar-EG"));
+    try {
+      GraphiteNamePattern pattern = new GraphiteNamePattern("org.test.controller.*.status.*");
+      Assertions.assertThat(pattern.extractParameters("org.test.controller.gather.status.400"))
+          .containsOnlyKeys("${0}", "${1}");
+    } finally {
+      Locale.setDefault(defaultLocale);
+    }
+  }
+
   @Test
   void extractParameters_WHEN_emptyStringInDottedMetricsName_THEN_ShouldReturnEmptyString() {
     GraphiteNamePattern pattern;