Extract logic from view to helper or controller

The following discussion from !162833 (merged) should be addressed:

• @ddieulivol started a discussion: (+2 comments)

  note (non-blocking): Ideally, we would have this logic in a helper method or in the controller instead of directly in the view:

  # Before
  @last_elasticsearch_reindexing_task.subtasks.order_by_alias_name_asc.each do |subtask|
  
  # After
  @last_task_subtasks.each do |subtask|

  We could then get rid of this mock altogether.

        assign(:last_task_subtasks, task)

  I didn't do this refactoring, as I didn't want to change too many things.