Removes EE differences for pipelines/index.html

Moves shared runner partial behind render_if_exists
Creates a new file for the flash message content to
avoid differences between CE and EE

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

 - @no_container = true
 - page_title "Pipelines"
 
-= content_for :flash_message do
-  = render 'shared/shared_runners_minutes_limit', project: @project
+= render_if_exists "shared/shared_runners_minutes_limit_flash_message"
 
 %div{ 'class' => container_class }
   #pipelines-list-vue{ data: { endpoint: project_pipelines_path(@project, format: :json),

ee/app/views/shared/_shared_runners_minutes_limit_flash_message.html.haml

+= content_for :flash_message do
+  = render 'shared/shared_runners_minutes_limit', project: @project