Show how long this pipeline was queued

Closes #19804

app/models/ci/pipeline.rb

@@ -257,6 +257,13 @@ module Ci
       ]
     end
 
+    def queued_duration
+      return unless started_at
+
+      seconds = (started_at - created_at).to_i
+      seconds unless seconds.zero?
+    end
+
     def update_duration
       return unless started_at
 

app/views/projects/pipelines/_info.html.haml

@@ -10,6 +10,9 @@
   - if @pipeline.duration
     in
     = time_interval_in_words(@pipeline.duration)
+  - if @pipeline.queued_duration
+    (queued for
+    = "#{time_interval_in_words(@pipeline.queued_duration)})"
 
   .pull-right
     = link_to namespace_project_pipeline_path(@project.namespace, @project, @pipeline), class: "ci-status ci-#{@pipeline.status}" do