metrics: enable input metrics by default

Signed-off-by: Shizuo Fujita <fujita@clear-code.com>

Author: Watson1978

lib/fluent/root_agent.rb

@@ -86,7 +86,7 @@ def initialize(log:, system_config: SystemConfig.new, start_in_parallel: false)
       @without_source = system_config.without_source || false
       @source_only_mode = SourceOnlyMode.new(system_config.with_source_only, start_in_parallel)
       @source_only_buffer_agent = nil
-      @enable_input_metrics = system_config.enable_input_metrics || false
+      @enable_input_metrics = system_config.enable_input_metrics
 
       suppress_interval(system_config.emit_error_log_interval) unless system_config.emit_error_log_interval.nil?
     end

lib/fluent/supervisor.rb

@@ -632,7 +632,7 @@ def self.default_options
         without_source: nil,
         with_source_only: nil,
         enable_input_metrics: nil,
-        enable_size_metrics: nil,
+        enable_size_metrics: true,
         use_v1_config: true,
         strict_config_value: nil,
         supervise: true,

lib/fluent/system_config.rb

@@ -51,7 +51,7 @@ class SystemConfig
     config_param :strict_config_value, :bool, default: nil
     config_param :enable_msgpack_time_support, :bool, default: nil
     config_param :disable_shared_socket, :bool, default: nil
-    config_param :enable_input_metrics, :bool, default: nil
+    config_param :enable_input_metrics, :bool, default: true
     config_param :enable_size_metrics, :bool, default: nil
     config_param :enable_jit, :bool, default: false
     config_param :file_permission, default: nil do |v|