add public api doc

Author: mutianf

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/stub/metrics/BuiltinMetricsView.java

@@ -105,6 +105,10 @@ public static void registerBuiltinMetrics(
         credentials, builder, endpoint, Credentials.GOOGLE_DEFAULT_UNIVERSE, null);
   }
 
+  /**
+   * Register built-in metrics on the {@link SdkMeterProviderBuilder} with custom credentials,
+   * endpoint and executor service.
+   */
   public static void registerBuiltinMetrics(
       @Nullable Credentials credentials,
       SdkMeterProviderBuilder builder,

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/stub/metrics/CustomOpenTelemetryMetricsProvider.java

@@ -86,13 +86,17 @@ public static void setupSdkMeterProvider(SdkMeterProviderBuilder builder, String
     setupSdkMeterProvider(builder, null, endpoint);
   }
 
-  /** Convenient method to set up SdkMeterProviderBuilder with a custom credentials and endpoint. */
+  /** Convenient method to set up SdkMeterProviderBuilder with custom credentials and endpoint. */
   public static void setupSdkMeterProvider(
       SdkMeterProviderBuilder builder, Credentials credentials, String endpoint)
       throws IOException {
     BuiltinMetricsView.registerBuiltinMetrics(credentials, builder, endpoint);
   }
 
+  /**
+   * Convenient method to set up SdkMeterProviderBuilder with custom credentials, endpoint and
+   * executor service.
+   */
   public static void setupSdkMeterProvider(
       SdkMeterProviderBuilder builder,
       Credentials credentials,