Fix empty node stats pipelines (#17185)

Fixed an issue where the `/_node/stats` API displayed empty pipeline metrics 
when X-Pack monitoring was enabled

Author: kaisecheng

Diff for: logstash-core/lib/logstash/api/commands/stats.rb

@@ -185,9 +185,9 @@ def report(stats, extended_stats = nil, opts = {})
               :reloads => stats[:reloads],
               :queue => stats[:queue],
               :pipeline => {
-                :workers => stats[:config][:workers],
-                :batch_size => stats[:config][:batch_size],
-                :batch_delay => stats[:config][:batch_delay],
+                :workers => stats.dig(:config, :workers),
+                :batch_size => stats.dig(:config, :batch_size),
+                :batch_delay => stats.dig(:config, :batch_delay),
               }
             }
             ret[:dead_letter_queue] = stats[:dlq] if stats.include?(:dlq)

Diff for: qa/integration/services/monitoring_api.rb

@@ -31,6 +31,12 @@ def pipeline_stats(pipeline_id)
     stats_response.fetch("pipelines").fetch(pipeline_id)
   end
 
+  def pipelines_stats
+    resp = Manticore.get("http://localhost:#{@port}/_node/stats/pipelines").body
+    stats_response = JSON.parse(resp)
+    stats_response.fetch("pipelines")
+  end
+
   def event_stats
     resp = Manticore.get("http://localhost:#{@port}/_node/stats").body
     stats_response = JSON.parse(resp)

Diff for: x-pack/qa/integration/monitoring/direct_shipping_spec.rb

@@ -31,6 +31,12 @@
 
   include_examples "record monitoring data to es"
 
+  it "gives pipelines stats" do
+    api = MonitoringAPI.new
+    stats = api.pipelines_stats
+    expect(stats.keys).not_to be_nil
+  end
+
   after :all do
     @logstash_service.stop unless @logstash_service.nil?
     @elasticsearch_service.stop unless @elasticsearch_service.nil?