Add invalid builds counter metric to stage seeds class

lib/gitlab/ci/stage/seed.rb

@@ -39,6 +39,10 @@ module Gitlab
           pipeline.stages.create!(stage).tap do |stage|
             builds_attributes = builds.map do |attributes|
               attributes.merge(stage_id: stage.id)
+
+              if attributes.fetch(:stage_id).nil?
+                invalid_builds_counter.increment(node: hostname)
+              end
             end
 
             pipeline.builds.create!(builds_attributes).each do |build|
@@ -52,6 +56,15 @@ module Gitlab
         def protected_ref?
           @protected_ref ||= project.protected_for?(pipeline.ref)
         end
+
+        def invalid_builds_counter
+          @counter ||= Gitlab::Metrics.counter(:invalid_builds_counter,
+                                               'Builds without stage assigned counter')
+        end
+
+        def hostname
+          @hostname ||= Socket.gethostname
+        end
       end
     end
   end