Extract builds queue processing into a separate method

This commit extracts builds queue processing into a separate method.
This method will be used to actually execute a builds queuing query on
the database. Separate method makes it easier to instrument execution of
this expensive query.

app/services/ci/register_job_service.rb

@@ -110,7 +110,7 @@ module Ci
       end
 
       if Feature.enabled?(:ci_register_job_service_one_by_one, runner, default_enabled: true)
-        build_ids = builds.pluck(:id)
+        build_ids = process_queue(-> { builds.pluck(:id) })
 
         @metrics.observe_queue_size(-> { build_ids.size })
 
@@ -118,13 +118,19 @@ module Ci
           yield Ci::Build.find(build_id)
         end
       else
-        @metrics.observe_queue_size(-> { builds.to_a.size })
+        builds = process_queue(-> { builds.to_a })
+
+        @metrics.observe_queue_size(-> { builds.size })
 
         builds.each(&blk)
       end
     end
     # rubocop: enable CodeReuse/ActiveRecord
 
+    def process_queue(queue_query_proc)
+      queue_query_proc.call
+    end
+
     def process_build(build, params)
       unless build.pending?
         @metrics.increment_queue_operation(:build_not_pending)