metrics: add getter method automatically

Signed-off-by: Shizuo Fujita <[email protected]>

Author: Watson1978

lib/fluent/plugin_helper/metrics.rb

@@ -72,6 +72,12 @@ def metrics_create(namespace: "fluentd", subsystem: "metrics", name:, help_text:
 
         @_metrics["#{@plugin_type_or_id}_#{namespace}_#{subsystem}_#{name}"] = metrics
 
+        singleton_class.module_eval do
+          unless method_defined?(name)
+            define_method(name) { metrics.get }
+          end
+        end
+
         metrics
       end